libsimgear-dev 3.4.0-3 / usr / include / simgear / props / props.hxx

/**
 * \file props.hxx
 * Interface definition for a property list.
 * Started Fall 2000 by David Megginson, david@megginson.com
 * This code is released into the Public Domain.
 *
 * See props.html for documentation [replace with URL when available].
 *
 * $Id$
 */

#ifndef __PROPS_HXX
#define __PROPS_HXX

#ifndef PROPS_STANDALONE
#define PROPS_STANDALONE 0
#endif

#include <vector>
#include <string>
#include <iostream>
#include <sstream>
#include <typeinfo>

#include <boost/utility.hpp>
#include <boost/type_traits/is_enum.hpp>

#if PROPS_STANDALONE
#else
#include <simgear/compiler.h>
#include <simgear/debug/logstream.hxx>
#endif


#include <simgear/math/SGMathFwd.hxx>
#include <simgear/math/sg_types.hxx>
#include <simgear/structure/SGReferenced.hxx>
#include <simgear/structure/SGSharedPtr.hxx>

// XXX This whole file should be in the simgear namespace, but I don't
// have the guts yet...

namespace simgear
{

  class PropertyInterpolationMgr;

template<typename T>
std::istream& readFrom(std::istream& stream, T& result)
{
    stream >> result;
    return stream;
}

/**
 * Parse a string as an object of a given type.
 * XXX no error behavior yet.
 *
 * @tparam T the return type
 * @param str the string
 * @return the object.
 */
template<typename T>
inline T parseString(const std::string& str)
{
    std::istringstream stream(str);
    T result;
    readFrom(stream, result);
    return result;
}

/**
 * Property value types.
 */

#ifdef NONE
#pragma warn A sloppy coder has defined NONE as a macro!
#undef NONE
#endif

#ifdef ALIAS
#pragma warn A sloppy coder has defined ALIAS as a macro!
#undef ALIAS
#endif

#ifdef UNSPECIFIED
#pragma warn A sloppy coder has defined UNSPECIFIED as a macro!
#undef UNSPECIFIED
#endif

#ifdef BOOL
#pragma warn A sloppy coder has defined BOOL as a macro!
#undef BOOL
#endif

#ifdef INT
#pragma warn A sloppy coder has defined INT as a macro!
#undef INT
#endif

#ifdef LONG
#pragma warn A sloppy coder has defined LONG as a macro!
#undef LONG
#endif

#ifdef FLOAT
#pragma warn A sloppy coder has defined FLOAT as a macro!
#undef FLOAT
#endif

#ifdef DOUBLE
#pragma warn A sloppy coder has defined DOUBLE as a macro!
#undef DOUBLE
#endif

#ifdef STRING
#pragma warn A sloppy coder has defined STRING as a macro!
#undef STRING
#endif

namespace props
{
/**
 * The possible types of an SGPropertyNode. Types that appear after
 * EXTENDED are not stored in the SGPropertyNode itself.
 */
enum Type {
    NONE = 0, /**< The node hasn't been assigned a value yet. */
    ALIAS, /**< The node "points" to another node. */
    BOOL,
    INT,
    LONG,
    FLOAT,
    DOUBLE,
    STRING,
    UNSPECIFIED,
    EXTENDED, /**< The node's value is not stored in the property;
               * the actual value and type is retrieved from an
               * SGRawValue node. This type is never returned by @see
               * SGPropertyNode::getType.
               */
    // Extended properties
    VEC3D,
    VEC4D
};

template<typename T> struct PropertyTraits;

#define DEFINTERNALPROP(TYPE, PROP) \
template<> \
struct PropertyTraits<TYPE> \
{ \
    static const Type type_tag = PROP; \
    enum  { Internal = 1 }; \
}

DEFINTERNALPROP(bool, BOOL);
DEFINTERNALPROP(int, INT);
DEFINTERNALPROP(long, LONG);
DEFINTERNALPROP(float, FLOAT);
DEFINTERNALPROP(double, DOUBLE);
DEFINTERNALPROP(const char *, STRING);
DEFINTERNALPROP(const char[], STRING);
#undef DEFINTERNALPROP

}
}



////////////////////////////////////////////////////////////////////////
// A raw value.
//
// This is the mechanism that information-providing routines can
// use to link their own values to the property manager.  Any
// SGValue can be tied to a raw value and then untied again.
//
// Note: we are forced to use inlined methods here to ensure
// that the templates will be instantiated.  We're probably taking
// a small performance hit for that.
////////////////////////////////////////////////////////////////////////

/**
 * Base class for SGRawValue classes that holds no type
 * information. This allows some generic manipulation of the
 * SGRawValue object.
 */
class SGRaw
{
public:
    /**
     * Get the type enumeration for the raw value.
     *
     * @return the type.
     */
    virtual simgear::props::Type getType() const = 0;
    virtual ~SGRaw() {}
    
    /**
     * Create a new deep copy of this raw value.
     *
     * The copy will contain its own version of the underlying value
     * as well, and will be the same type.
     *
     * @return A deep copy of the current object.
     */
    virtual SGRaw* clone() const = 0;

};

class SGRawExtended : public SGRaw
{
public:
    /**    
     * Make an SGRawValueContainer from the SGRawValue.
     *
     * This is a virtual function of SGRawExtended so that
     * SGPropertyNode::untie doesn't need to know the type of an
     * extended property.
     */
    virtual SGRawExtended* makeContainer() const = 0;
    /**
     * Write value out to a stream
     */
    virtual std::ostream& printOn(std::ostream& stream) const = 0;
    /**
     * Read value from a stream and store it.
     */
    virtual std::istream& readFrom(std::istream& stream) = 0;
};

// Choose between different base classes based on whether the value is
// stored internal to the property node. This frees us from defining
// the virtual functions in the SGRawExtended interface where they
// don't make sense, e.g. readFrom for the const char* type.
template<typename T, int internal = simgear::props::PropertyTraits<T>::Internal>
class SGRawBase;

template<typename T>
class SGRawBase<T, 1> : public SGRaw
{
};

template<typename T>
class SGRawBase<T, 0> : public SGRawExtended
{
    virtual SGRawExtended* makeContainer() const;
    virtual std::ostream& printOn(std::ostream& stream) const;
    virtual std::istream& readFrom(std::istream& stream);
};

/**
 * Abstract base class for a raw value.
 *
 * The property manager is implemented in two layers. The SGPropertyNode is the
 * highest and most abstract layer, representing an LValue/RValue pair: it
 * records the position of the property in the property tree and contains
 * facilities for navigation to other nodes. It is guaranteed to be persistent:
 * the SGPropertyNode will not change during a session, even if the property is
 * bound and unbound multiple times.
 *
 * When the property value is not managed internally in the
 * SGPropertyNode, the SGPropertyNode will contain a reference to an
 * SGRawValue (this class), which provides an abstract way to get,
 * set, and clone the underlying value.  The SGRawValue may change
 * frequently during a session as a value is retyped or bound and
 * unbound to various data source, but the abstract SGPropertyNode
 * layer insulates the application from those changes.
 *
 * The SGPropertyNode class always keeps a *copy* of a raw value, not the
 * original one passed to it; if you override a derived class but do not replace
 * the {@link SGRaw::clone clone()} method, strange things will happen.
 *
 * All derived SGRawValue classes must implement getValue(), setValue(), and
 * {@link SGRaw::clone clone()} for the appropriate type.
 *
 * @see SGPropertyNode
 * @see SGRawValuePointer
 * @see SGRawValueFunctions
 * @see SGRawValueFunctionsIndexed
 * @see SGRawValueMethods
 * @see SGRawValueMethodsIndexed
 * @see SGRawValueContainer
 */
template <class T>
class SGRawValue : public SGRawBase<T>
{
public:

  /**
   * The default underlying value for this type.
   *
   * Every raw value has a default; the default is false for a
   * boolean, 0 for the various numeric values, and "" for a string.
   * If additional types of raw values are added in the future, they
   * may need different kinds of default values (such as epoch for a
   * date type).  The default value is used when creating new values.
   */
  static T DefaultValue()
  {
    return T();
  }


  /**
   * Constructor.
   *
   * Use the default value for this type.
   */
  SGRawValue () {}


  /**
   * Destructor.
   */
  virtual ~SGRawValue () {}


  /**
   * Return the underlying value.
   *
   * @return The actual value for the property.
   * @see #setValue
   */
  virtual T getValue () const = 0;


  /**
   * Assign a new underlying value.
   *
   * If the new value cannot be set (because this is a read-only
   * raw value, or because the new value is not acceptable for
   * some reason) this method returns false and leaves the original
   * value unchanged.
   *
   * @param value The actual value for the property.
   * @return true if the value was set successfully, false otherwise.
   * @see #getValue
   */
  virtual bool setValue (T value) = 0;


  /**
   * Return the type tag for this raw value type.
   */
  virtual simgear::props::Type getType() const
  {
    return simgear::props::PropertyTraits<T>::type_tag;
  }
};



////////////////////////////////////////////////////////////////////////
// Default values for every type.
////////////////////////////////////////////////////////////////////////

template<> inline bool SGRawValue<bool>::DefaultValue()
{
  return false;
}

template<> inline const char * SGRawValue<const char *>::DefaultValue()
{
  return "";
}

/**
 * A raw value bound to a pointer.
 *
 * This is the most efficient way to tie an external value, but also
 * the most dangerous, because there is no way for the supplier to
 * perform bounds checking and derived calculations except by polling
 * the variable to see if it has changed.  There is no default
 * constructor, because this class would be meaningless without a
 * pointer.
 */
template <class T>
class SGRawValuePointer : public SGRawValue<T>
{
public:

  /**
   * Explicit pointer constructor.
   *
   * Create a new raw value bound to the value of the variable
   * referenced by the pointer.
   *
   * @param ptr The pointer to the variable to which this raw value
   * will be bound.
   */
  SGRawValuePointer (T * ptr) : _ptr(ptr) {}

  /**
   * Destructor.
   */
  virtual ~SGRawValuePointer () {}

  /**
   * Get the underlying value.
   *
   * This method will dereference the pointer and return the
   * variable's value.
   */
  virtual T getValue () const { return *_ptr; }

  /**
   * Set the underlying value.
   *
   * This method will dereference the pointer and change the
   * variable's value.
   */
  virtual bool setValue (T value) { *_ptr = value; return true; }

  /**
   * Create a copy of this raw value.
   *
   * The copy will use the same external pointer as the original.
   */
  virtual SGRaw* clone () const {
    return new SGRawValuePointer(_ptr);
  }

private:
  T * _ptr;
};


/**
 * A value managed through static functions.
 *
 * A read-only value will not have a setter; a write-only value will
 * not have a getter.
 */
template <class T>
class SGRawValueFunctions : public SGRawValue<T>
{
public:

  /**
   * The template type of a static getter function.
   */
  typedef T (*getter_t)();

  /**
   * The template type of a static setter function.
   */
  typedef void (*setter_t)(T);

  /**
   * Explicit constructor.
   *
   * Create a new raw value bound to the getter and setter supplied.
   *
   * @param getter A static function for getting a value, or 0
   * to read-disable the value.
   * @param setter A static function for setting a value, or 0
   * to write-disable the value.
   */
  SGRawValueFunctions (getter_t getter = 0, setter_t setter = 0)
    : _getter(getter), _setter(setter) {}

  /**
   * Destructor.
   */
  virtual ~SGRawValueFunctions () {}

  /**
   * Get the underlying value.
   *
   * This method will invoke the getter function to get a value.
   * If no getter function was supplied, this method will always
   * return the default value for the type.
   */
  virtual T getValue () const {
    if (_getter) return (*_getter)();
    else return SGRawValue<T>::DefaultValue();
  }

  /**
   * Set the underlying value.
   *
   * This method will invoke the setter function to change the
   * underlying value.  If no setter function was supplied, this
   * method will return false.
   */
  virtual bool setValue (T value) {
    if (_setter) { (*_setter)(value); return true; }
    else return false;
  }

  /**
   * Create a copy of this raw value, bound to the same functions.
   */
  virtual SGRaw* clone () const {
    return new SGRawValueFunctions(_getter,_setter);
  }

private:
  getter_t _getter;
  setter_t _setter;
};


/**
 * An indexed value bound to static functions.
 *
 * A read-only value will not have a setter; a write-only value will
 * not have a getter.  An indexed value is useful for binding one
 * of a list of possible values (such as multiple engines for a
 * plane).  The index is hard-coded at creation time.
 *
 * @see SGRawValue
 */
template <class T>
class SGRawValueFunctionsIndexed : public SGRawValue<T>
{
public:
  typedef T (*getter_t)(int);
  typedef void (*setter_t)(int,T);
  SGRawValueFunctionsIndexed (int index, getter_t getter = 0, setter_t setter = 0)
    : _index(index), _getter(getter), _setter(setter) {}
  virtual ~SGRawValueFunctionsIndexed () {}
  virtual T getValue () const {
    if (_getter) return (*_getter)(_index);
    else return SGRawValue<T>::DefaultValue();
  }
  virtual bool setValue (T value) {
    if (_setter) { (*_setter)(_index, value); return true; }
    else return false;
  }
  virtual SGRaw* clone () const {
    return new SGRawValueFunctionsIndexed(_index, _getter, _setter);
  }
private:
  int _index;
  getter_t _getter;
  setter_t _setter;
};


/**
 * A value managed through an object and access methods.
 *
 * A read-only value will not have a setter; a write-only value will
 * not have a getter.
 */
template <class C, class T>
class SGRawValueMethods : public SGRawValue<T>
{
public:
  typedef T (C::*getter_t)() const;
  typedef void (C::*setter_t)(T);
  SGRawValueMethods (C &obj, getter_t getter = 0, setter_t setter = 0)
    : _obj(obj), _getter(getter), _setter(setter) {}
  virtual ~SGRawValueMethods () {}
  virtual T getValue () const {
    if (_getter) { return (_obj.*_getter)(); }
    else { return SGRawValue<T>::DefaultValue(); }
  }
  virtual bool setValue (T value) {
    if (_setter) { (_obj.*_setter)(value); return true; }
    else return false;
  }
  virtual SGRaw* clone () const {
    return new SGRawValueMethods(_obj, _getter, _setter);
  }
private:
  C &_obj;
  getter_t _getter;
  setter_t _setter;
};


/**
 * An indexed value managed through an object and access methods.
 *
 * A read-only value will not have a setter; a write-only value will
 * not have a getter.
 */
template <class C, class T>
class SGRawValueMethodsIndexed : public SGRawValue<T>
{
public:
  typedef T (C::*getter_t)(int) const;
  typedef void (C::*setter_t)(int, T);
  SGRawValueMethodsIndexed (C &obj, int index,
		     getter_t getter = 0, setter_t setter = 0)
    : _obj(obj), _index(index), _getter(getter), _setter(setter) {}
  virtual ~SGRawValueMethodsIndexed () {}
  virtual T getValue () const {
    if (_getter) { return (_obj.*_getter)(_index); }
    else { return SGRawValue<T>::DefaultValue(); }
  }
  virtual bool setValue (T value) {
    if (_setter) { (_obj.*_setter)(_index, value); return true; }
    else return false;
  }
  virtual SGRaw* clone () const {
    return new SGRawValueMethodsIndexed(_obj, _index, _getter, _setter);
  }
private:
  C &_obj;
  int _index;
  getter_t _getter;
  setter_t _setter;
};

/**
 * A raw value that contains its value. This provides a way for
 * property nodes to contain values that shouldn't be stored in the
 * property node itself.
 */
template <class T>
class SGRawValueContainer : public SGRawValue<T>
{
public:

    /**
     * Explicit constructor.
     */
    SGRawValueContainer(const T& obj) : _obj(obj) {}

    /**
     * Destructor.
     */
    virtual ~SGRawValueContainer() {}

    /**
     * Get the underlying value.
     */
    virtual T getValue() const { return _obj; }

    /**
     * Set the underlying value.
     *
     * This method will dereference the pointer and change the
     * variable's value.
     */
    virtual bool setValue (T value) { _obj = value; return true; }

    /**
     * Create a copy of this raw value.
     */
    virtual SGRaw* clone () const {
        return new SGRawValueContainer(_obj);
    }

private:
    T _obj;
};

template<typename T>
SGRawExtended* SGRawBase<T, 0>::makeContainer() const
{
    return new SGRawValueContainer<T>(static_cast<const SGRawValue<T>*>(this)
                                      ->getValue());
}

template<typename T>
std::ostream& SGRawBase<T, 0>::printOn(std::ostream& stream) const
{
    return stream << static_cast<SGRawValue<T>*>(this)->getValue();
}

template<typename T>
std::istream& SGRawBase<T, 0>::readFrom(std::istream& stream)
{
    T value;
    simgear::readFrom(stream, value);
    static_cast<SGRawValue<T>*>(this)->setValue(value);
    return stream;
}

/**
 * The smart pointer that manage reference counting
 */
class SGPropertyNode;
typedef SGSharedPtr<SGPropertyNode> SGPropertyNode_ptr;
typedef SGSharedPtr<const SGPropertyNode> SGConstPropertyNode_ptr;

namespace simgear
{
typedef std::vector<SGPropertyNode_ptr> PropertyList;
}

/**
 * The property change listener interface.
 *
 * <p>Any class that needs to listen for property changes must implement
 * this interface.</p>
 */
class SGPropertyChangeListener
{
public:
  virtual ~SGPropertyChangeListener ();

  /// Called if value of \a node has changed.
  virtual void valueChanged(SGPropertyNode * node);

  /// Called if \a child has been added to the given \a parent.
  virtual void childAdded(SGPropertyNode * parent, SGPropertyNode * child);

  /// Called if \a child has been removed from its \a parent.
  virtual void childRemoved(SGPropertyNode * parent, SGPropertyNode * child);

protected:
  friend class SGPropertyNode;
  virtual void register_property (SGPropertyNode * node);
  virtual void unregister_property (SGPropertyNode * node);

private:
  std::vector<SGPropertyNode *> _properties;
};


/**
 * A node in a property tree.
 */
class SGPropertyNode : public SGReferenced
{
public:

  /**
   * Public constants.
   */
  enum {
    MAX_STRING_LEN = 1024
  };

  /**
   * Access mode attributes.
   *
   * <p>The ARCHIVE attribute is strictly advisory, and controls
   * whether the property should normally be saved and restored.</p>
   */
  enum Attribute {
    NO_ATTR = 0,
    READ = 1,
    WRITE = 2,
    ARCHIVE = 4,
    REMOVED = 8,
    TRACE_READ = 16,
    TRACE_WRITE = 32,
    USERARCHIVE = 64,
    PRESERVE = 128
    // beware: if you add another attribute here,
    // also update value of "LAST_USED_ATTRIBUTE".
  };


  /**
   * Last used attribute
   * Update as needed when enum Attribute is changed
   */
  static const int LAST_USED_ATTRIBUTE;

  /**
   * Default constructor.
   */
  SGPropertyNode ();


  /**
   * Copy constructor.
   */
  SGPropertyNode (const SGPropertyNode &node);


  /**
   * Destructor.
   */
  virtual ~SGPropertyNode ();



  //
  // Basic properties.
  //

  /**
   * Test whether this node contains a primitive leaf value.
   */
    bool hasValue () const { return (_type != simgear::props::NONE); }


  /**
   * Get the node's simple (XML) name.
   */
  const char * getName () const { return _name.c_str(); }

  /**
   * Get the node's simple name as a string.
   */
  const std::string& getNameString () const { return _name; }

  /**
   * Get the node's pretty display name, with subscript when needed.
   */
    std::string getDisplayName (bool simplify = false) const;


  /**
   * Get the node's integer index.
   */
  int getIndex () const { return _index; }


  /**
   * Get a non-const pointer to the node's parent.
   */
  SGPropertyNode * getParent () { return _parent; }


  /**
   * Get a const pointer to the node's parent.
   */
  const SGPropertyNode * getParent () const { return _parent; }


  //
  // Children.
  //


  /**
   * Get the number of child nodes.
   */
  int nChildren () const { return (int)_children.size(); }


  /**
   * Get a child node by position (*NOT* index).
   */
  SGPropertyNode * getChild (int position);


  /**
   * Get a const child node by position (*NOT* index).
   */
  const SGPropertyNode * getChild (int position) const;


  /**
   * Test whether a named child exists.
   */
  bool hasChild (const char * name, int index = 0) const
  {
    return (getChild(name, index) != 0);
  }

  /**
   * Test whether a named child exists.
   */
  bool hasChild (const std::string& name, int index = 0) const
  {
    return (getChild(name, index) != 0);
  }

  /**
   * Create a new child node with the given name and an unused index
   *
   * @param min_index Minimal index for new node (skips lower indices)
   * @param append    Whether to simply use the index after the last used index
   *                  or use a lower, unused index if it exists
   */
  SGPropertyNode * addChild ( const char* name,
                              int min_index = 0,
                              bool append = true );
  SGPropertyNode * addChild ( const std::string& name,
                              int min_index = 0,
                              bool append = true )
  { return addChild(name.c_str(), min_index, append); }

  /**
   * Create multiple child nodes with the given name an unused indices
   *
   * @param count     The number of nodes create
   * @param min_index Minimal index for new nodes (skips lower indices)
   * @param append    Whether to simply use the index after the last used index
   *                  or use a lower, unused index if it exists
   */
  simgear::PropertyList addChildren ( const std::string& name,
                                      size_t count,
                                      int min_index = 0,
                                      bool append = true );

  /**
   * Get a child node by name and index.
   */
  SGPropertyNode * getChild (const char* name, int index = 0,
                             bool create = false);
  SGPropertyNode * getChild (const std::string& name, int index = 0,
                             bool create = false);
  /**
   * Get a const child node by name and index.
   */
  const SGPropertyNode * getChild (const char * name, int index = 0) const;

  /**
   * Get a const child node by name and index.
   */
  const SGPropertyNode * getChild (const std::string& name, int index = 0) const
  { return getChild(name.c_str(), index); }


  /**
   * Get a vector of all children with the specified name.
   */
  simgear::PropertyList getChildren (const char * name) const;

  /**
   * Get a vector of all children with the specified name.
   */
  simgear::PropertyList getChildren (const std::string& name) const
  { return getChildren(name.c_str()); }

  /**
   * Remove child by pointer (if it is a child of this node).
   *
   * @return true, if the node was deleted.
   */
  bool removeChild(SGPropertyNode* node);

  // TODO do we need the removeXXX methods to return the deleted nodes?
  /**
   * Remove child by position.
   */
  SGPropertyNode_ptr removeChild(int pos);


  /**
   * Remove a child node
   */
  SGPropertyNode_ptr removeChild(const char * name, int index = 0);

  /**
   * Remove a child node
   */
  SGPropertyNode_ptr removeChild(const std::string& name, int index = 0)
  { return removeChild(name.c_str(), index); }

  /**
   * Remove all children with the specified name.
   */
  simgear::PropertyList removeChildren(const char * name);

  /**
   * Remove all children with the specified name.
   */
  simgear::PropertyList removeChildren(const std::string& name)
  { return removeChildren(name.c_str()); }

  /**
   * Remove all children (does not change the value of the node)
   */
  void removeAllChildren();

  //
  // Alias support.
  //


  /**
   * Alias this node's leaf value to another's.
   */
  bool alias (SGPropertyNode * target);


  /**
   * Alias this node's leaf value to another's by relative path.
   */
  bool alias (const char * path);

  /**
   * Alias this node's leaf value to another's by relative path.
   */
  bool alias (const std::string& path)
  { return alias(path.c_str()); }


  /**
   * Remove any alias for this node.
   */
  bool unalias ();


  /**
   * Test whether the node's leaf value is aliased to another's.
   */
  bool isAlias () const { return (_type == simgear::props::ALIAS); }


  /**
   * Get a non-const pointer to the current alias target, if any.
   */
  SGPropertyNode * getAliasTarget ();


  /**
   * Get a const pointer to the current alias target, if any.
   */
  const SGPropertyNode * getAliasTarget () const;


  //
  // Path information.
  //


  /**
   * Get the path to this node from the root.
   */
  std::string getPath (bool simplify = false) const;


  /**
   * Get a pointer to the root node.
   */
  SGPropertyNode * getRootNode ();


  /**
   * Get a const pointer to the root node.
   */
  const SGPropertyNode * getRootNode () const;


  /**
   * Get a pointer to another node by relative path.
   */
  SGPropertyNode * getNode (const char * relative_path, bool create = false);

  /**
   * Get a pointer to another node by relative path.
   */
  SGPropertyNode * getNode (const std::string& relative_path, bool create = false)
  { return getNode(relative_path.c_str(), create); }

  /**
   * Get a pointer to another node by relative path.
   *
   * This method leaves the index off the last member of the path,
   * so that the user can specify it separately (and save some
   * string building).  For example, getNode("/bar[1]/foo", 3) is
   * exactly equivalent to getNode("bar[1]/foo[3]").  The index
   * provided overrides any given in the path itself for the last
   * component.
   */
  SGPropertyNode * getNode (const char * relative_path, int index,
			    bool create = false);

  /**
   * Get a pointer to another node by relative path.
   *
   * This method leaves the index off the last member of the path,
   * so that the user can specify it separately (and save some
   * string building).  For example, getNode("/bar[1]/foo", 3) is
   * exactly equivalent to getNode("bar[1]/foo[3]").  The index
   * provided overrides any given in the path itself for the last
   * component.
   */
  SGPropertyNode * getNode (const std::string& relative_path, int index,
			    bool create = false)
  { return getNode(relative_path.c_str(), index, create); }

  /**
   * Get a const pointer to another node by relative path.
   */
  const SGPropertyNode * getNode (const char * relative_path) const;

  /**
   * Get a const pointer to another node by relative path.
   */
  const SGPropertyNode * getNode (const std::string& relative_path) const
  { return getNode(relative_path.c_str()); }


  /**
   * Get a const pointer to another node by relative path.
   *
   * This method leaves the index off the last member of the path,
   * so that the user can specify it separate.
   */
  const SGPropertyNode * getNode (const char * relative_path,
				  int index) const;

  /**
   * Get a const pointer to another node by relative path.
   *
   * This method leaves the index off the last member of the path,
   * so that the user can specify it separate.
   */
  const SGPropertyNode * getNode (const std::string& relative_path,
				  int index) const
  { return getNode(relative_path.c_str(), index); }

  //
  // Access Mode.
  //

  /**
   * Check a single mode attribute for the property node.
   */
  bool getAttribute (Attribute attr) const { return ((_attr & attr) != 0); }


  /**
   * Set a single mode attribute for the property node.
   */
  void setAttribute (Attribute attr, bool state) {
    (state ? _attr |= attr : _attr &= ~attr);
  }


  /**
   * Get all of the mode attributes for the property node.
   */
  int getAttributes () const { return _attr; }


  /**
   * Set all of the mode attributes for the property node.
   */
  void setAttributes (int attr) { _attr = attr; }
  

  //
  // Leaf Value (primitive).
  //


  /**
   * Get the type of leaf value, if any, for this node.
   */
  simgear::props::Type getType () const;


  /**
   * Get a bool value for this node.
   */
  bool getBoolValue () const;


  /**
   * Get an int value for this node.
   */
  int getIntValue () const;


  /**
   * Get a long int value for this node.
   */
  long getLongValue () const;


  /**
   * Get a float value for this node.
   */
  float getFloatValue () const;


  /**
   * Get a double value for this node.
   */
  double getDoubleValue () const;


  /**
   * Get a string value for this node.
   */
  const char * getStringValue () const;

  /**
   * Get a value from a node. If the actual type of the node doesn't
   * match the desired type, a conversion isn't guaranteed.
   */
  template<typename T>
  T getValue(typename boost::enable_if_c<simgear::props::PropertyTraits<T>::Internal>
             ::type* dummy = 0) const;
  // Getter for extended property
  template<typename T>
  T getValue(typename boost::disable_if_c<simgear::props::PropertyTraits<T>::Internal>
             ::type* dummy = 0) const;

  /**
   * Get a list of values from all children with the given name
   */
  template<typename T, typename T_get /* = T */> // TODO use C++11 or traits
  std::vector<T> getChildValues(const std::string& name) const;

  /**
   * Get a list of values from all children with the given name
   */
  template<typename T>
  std::vector<T> getChildValues(const std::string& name) const;

  /**
   * Set a bool value for this node.
   */
  bool setBoolValue (bool value);


  /**
   * Set an int value for this node.
   */
  bool setIntValue (int value);


  /**
   * Set a long int value for this node.
   */
  bool setLongValue (long value);


  /**
   * Set a float value for this node.
   */
  bool setFloatValue (float value);


  /**
   * Set a double value for this node.
   */
  bool setDoubleValue (double value);


  /**
   * Set a string value for this node.
   */
  bool setStringValue (const char * value);

  /**
   * Set a string value for this node.
   */
  bool setStringValue (const std::string& value)
  { return setStringValue(value.c_str()); }


  /**
   * Set a value of unspecified type for this node.
   */
  bool setUnspecifiedValue (const char * value);

  template<typename T>
  bool setValue(const T& val,
                typename boost::enable_if_c<simgear::props::PropertyTraits<T>::Internal>
                ::type* dummy = 0);

  template<typename T>
  bool setValue(const T& val,
                typename boost::disable_if_c<simgear::props::PropertyTraits<T>::Internal>
                ::type* dummy = 0);

  template<int N>
  bool setValue(const char (&val)[N])
  {
    return setValue(&val[0]);
  }
  
  /**
   * Set relative node to given value and afterwards make read only.
   *
   * @param relative_path   Path to node
   * @param value           Value to set
   *
   * @return whether value could be set
   */
  template<typename T>
  bool setValueReadOnly(const std::string& relative_path, const T& value)
  {
    SGPropertyNode* node = getNode(relative_path, true);
    bool ret = node->setValue(value);
    node->setAttributes(READ);
    return ret;
  }

  /**
   * Interpolate current value to target value within given time.
   *
   * @param type        Type of interpolation ("numeric", "color", etc.)
   * @param target      Node containing target value
   * @param duration    Duration of interpolation (in seconds)
   * @param easing      Easing function (http://easings.net/)
   */
  bool interpolate( const std::string& type,
                    const SGPropertyNode& target,
                    double duration = 0.6,
                    const std::string& easing = "swing" );

  /**
   * Interpolate current value to a series of values within given durations.
   *
   * @param type        Type of interpolation ("numeric", "color", etc.)
   * @param values      Nodes containing intermediate and target values
   * @param deltas      Durations for each interpolation step (in seconds)
   * @param easing      Easing function (http://easings.net/)
   */
  bool interpolate( const std::string& type,
                    const simgear::PropertyList& values,
                    const double_list& deltas,
                    const std::string& easing = "swing" );

  /**
   * Set the interpolation manager used by the interpolate methods.
   */
  static void setInterpolationMgr(simgear::PropertyInterpolationMgr* mgr);

  /**
   * Get the interpolation manager
   */
  static simgear::PropertyInterpolationMgr* getInterpolationMgr();

  /**
   * Print the value of the property to a stream.
   */
  std::ostream& printOn(std::ostream& stream) const;
  
  //
  // Data binding.
  //


  /**
   * Test whether this node is bound to an external data source.
   */
  bool isTied () const { return _tied; }

    /**
     * Bind this node to an external source.
     */
    template<typename T>
    bool tie(const SGRawValue<T> &rawValue, bool useDefault = true);

  /**
   * Unbind this node from any external data source.
   */
  bool untie ();


  //
  // Convenience methods using paths.
  // TODO: add attribute methods
  //


  /**
   * Get another node's type.
   */
  simgear::props::Type getType (const char * relative_path) const;

  /**
   * Get another node's type.
   */
  simgear::props::Type getType (const std::string& relative_path) const
  { return getType(relative_path.c_str()); }

  /**
   * Test whether another node has a leaf value.
   */
  bool hasValue (const char * relative_path) const;

  /**
   * Test whether another node has a leaf value.
   */
  bool hasValue (const std::string& relative_path) const
  { return hasValue(relative_path.c_str()); }

  /**
   * Get another node's value as a bool.
   */
  bool getBoolValue (const char * relative_path,
		     bool defaultValue = false) const;

  /**
   * Get another node's value as a bool.
   */
  bool getBoolValue (const std::string& relative_path,
		     bool defaultValue = false) const
  { return getBoolValue(relative_path.c_str(), defaultValue); }

  /**
   * Get another node's value as an int.
   */
  int getIntValue (const char * relative_path,
		   int defaultValue = 0) const;

  /**
   * Get another node's value as an int.
   */
  int getIntValue (const std::string& relative_path,
                   int defaultValue = 0) const
  { return getIntValue(relative_path.c_str(), defaultValue); }


  /**
   * Get another node's value as a long int.
   */
  long getLongValue (const char * relative_path,
		     long defaultValue = 0L) const;

  /**
   * Get another node's value as a long int.
   */
  long getLongValue (const std::string& relative_path,
		     long defaultValue = 0L) const
  { return getLongValue(relative_path.c_str(), defaultValue); }

  /**
   * Get another node's value as a float.
   */
  float getFloatValue (const char * relative_path,
		       float defaultValue = 0.0f) const;

  /**
   * Get another node's value as a float.
   */
  float getFloatValue (const std::string& relative_path,
		       float defaultValue = 0.0f) const
  { return getFloatValue(relative_path.c_str(), defaultValue); }


  /**
   * Get another node's value as a double.
   */
  double getDoubleValue (const char * relative_path,
			 double defaultValue = 0.0) const;

  /**
   * Get another node's value as a double.
   */
  double getDoubleValue (const std::string& relative_path,
			 double defaultValue = 0.0) const
  { return getDoubleValue(relative_path.c_str(), defaultValue); }

  /**
   * Get another node's value as a string.
   */
  const char * getStringValue (const char * relative_path,
			       const char * defaultValue = "") const;


  /**
   * Get another node's value as a string.
   */
  const char * getStringValue (const std::string& relative_path,
			       const char * defaultValue = "") const
  { return getStringValue(relative_path.c_str(), defaultValue); }


  /**
   * Set another node's value as a bool.
   */
  bool setBoolValue (const char * relative_path, bool value);

  /**
   * Set another node's value as a bool.
   */
  bool setBoolValue (const std::string& relative_path, bool value)
  { return setBoolValue(relative_path.c_str(), value); }


  /**
   * Set another node's value as an int.
   */
  bool setIntValue (const char * relative_path, int value);

  /**
   * Set another node's value as an int.
   */
  bool setIntValue (const std::string& relative_path, int value)
  { return setIntValue(relative_path.c_str(), value); }


  /**
   * Set another node's value as a long int.
   */
  bool setLongValue (const char * relative_path, long value);

  /**
   * Set another node's value as a long int.
   */
  bool setLongValue (const std::string& relative_path, long value)
  { return setLongValue(relative_path.c_str(), value); }


  /**
   * Set another node's value as a float.
   */
  bool setFloatValue (const char * relative_path, float value);

  /**
   * Set another node's value as a float.
   */
  bool setFloatValue (const std::string& relative_path, float value)
  { return setFloatValue(relative_path.c_str(), value); }


  /**
   * Set another node's value as a double.
   */
  bool setDoubleValue (const char * relative_path, double value);

  /**
   * Set another node's value as a double.
   */
  bool setDoubleValue (const std::string& relative_path, double value)
  { return setDoubleValue(relative_path.c_str(), value); }


  /**
   * Set another node's value as a string.
   */
  bool setStringValue (const char * relative_path, const char * value);

  bool setStringValue(const char * relative_path, const std::string& value)
  { return setStringValue(relative_path, value.c_str()); }
  /**
   * Set another node's value as a string.
   */
  bool setStringValue (const std::string& relative_path, const char * value)
  { return setStringValue(relative_path.c_str(), value); }

  bool setStringValue (const std::string& relative_path,
                       const std::string& value)
  { return setStringValue(relative_path.c_str(), value.c_str()); }

  /**
   * Set another node's value with no specified type.
   */
  bool setUnspecifiedValue (const char * relative_path, const char * value);


  /**
   * Test whether another node is bound to an external data source.
   */
  bool isTied (const char * relative_path) const;

  /**
   * Test whether another node is bound to an external data source.
   */
  bool isTied (const std::string& relative_path) const
  { return isTied(relative_path.c_str()); }

  /**
   * Bind another node to an external bool source.
   */
  bool tie (const char * relative_path, const SGRawValue<bool> &rawValue,
	    bool useDefault = true);

  /**
   * Bind another node to an external bool source.
   */
  bool tie (const std::string& relative_path, const SGRawValue<bool> &rawValue,
	    bool useDefault = true)
  { return tie(relative_path.c_str(), rawValue, useDefault); }


  /**
   * Bind another node to an external int source.
   */
  bool tie (const char * relative_path, const SGRawValue<int> &rawValue,
	    bool useDefault = true);

  /**
   * Bind another node to an external int source.
   */
  bool tie (const std::string& relative_path, const SGRawValue<int> &rawValue,
	    bool useDefault = true)
  { return tie(relative_path.c_str(), rawValue, useDefault); }


  /**
   * Bind another node to an external long int source.
   */
  bool tie (const char * relative_path, const SGRawValue<long> &rawValue,
	    bool useDefault = true);

  /**
   * Bind another node to an external long int source.
   */
  bool tie (const std::string& relative_path, const SGRawValue<long> &rawValue,
	    bool useDefault = true)
  { return tie(relative_path.c_str(), rawValue, useDefault); }


  /**
   * Bind another node to an external float source.
   */
  bool tie (const char * relative_path, const SGRawValue<float> &rawValue,
	    bool useDefault = true);

  /**
   * Bind another node to an external float source.
   */
  bool tie (const std::string& relative_path, const SGRawValue<float> &rawValue,
	    bool useDefault = true)
  { return tie(relative_path.c_str(), rawValue, useDefault); }


  /**
   * Bind another node to an external double source.
   */
  bool tie (const char * relative_path, const SGRawValue<double> &rawValue,
	    bool useDefault = true);

  /**
   * Bind another node to an external double source.
   */
  bool tie (const std::string& relative_path, const SGRawValue<double> &rawValue,
	    bool useDefault = true)
  { return tie(relative_path.c_str(), rawValue, useDefault); }


  /**
   * Bind another node to an external string source.
   */
  bool tie (const char * relative_path, const SGRawValue<const char *> &rawValue,
	    bool useDefault = true);

  /**
   * Bind another node to an external string source.
   */
  bool tie (const std::string& relative_path, const SGRawValue<const char*> &rawValue,
	    bool useDefault = true)
  { return tie(relative_path.c_str(), rawValue, useDefault); }


  /**
   * Unbind another node from any external data source.
   */
  bool untie (const char * relative_path);

  /**
   * Unbind another node from any external data source.
   */
  bool untie (const std::string& relative_path)
  { return untie(relative_path.c_str()); }


  /**
   * Add a change listener to the property. If "initial" is set call the
   * listener initially.
   */
  void addChangeListener (SGPropertyChangeListener * listener,
                          bool initial = false);


  /**
   * Remove a change listener from the property.
   */
  void removeChangeListener (SGPropertyChangeListener * listener);


  /**
   * Get the number of listeners.
   */
  int nListeners () const { return _listeners ? (int)_listeners->size() : 0; }


  /**
   * Fire a value change event to all listeners.
   */
  void fireValueChanged ();


  /**
   * Fire a child-added event to all listeners.
   */
  void fireChildAdded (SGPropertyNode * child);

  /**
   * Trigger a child-added and value-changed event for every child (Unlimited
   * depth).
   *
   * @param fire_self   Whether to trigger the events also for the node itself.
   *
   * It can be used to simulating the creation of a property tree, eg. for
   * (re)initializing a subsystem which is controlled through the property tree.
   */
  void fireCreatedRecursive(bool fire_self = false);

  /**
   * Fire a child-removed event to all listeners.
   */
  void fireChildRemoved (SGPropertyNode * child);

  /**
   * Fire a child-removed event for every child of this node (Unlimited depth)
   *
   * Upon removal of a child node only for this single node a child-removed
   * event is triggered. If eg. resource cleanup relies on receiving a
   * child-removed event for every child this method can be used.
   */
  void fireChildrenRemovedRecursive();


  /**
   * Clear any existing value and set the type to NONE.
   */
  void clearValue ();

  /**
   * Compare two property trees. The property trees are equal if: 1)
   * They have no children, and have the same type and the values are
   * equal, or 2) have the same number of children, and the
   * corresponding children in each tree are equal. "corresponding"
   * means have the same name and index.
   *
   * Attributes, removed children, and aliases aren't considered.
   */
  static bool compare (const SGPropertyNode& lhs, const SGPropertyNode& rhs);

protected:

  void fireValueChanged (SGPropertyNode * node);
  void fireChildAdded (SGPropertyNode * parent, SGPropertyNode * child);
  void fireChildRemoved (SGPropertyNode * parent, SGPropertyNode * child);

  SGPropertyNode_ptr eraseChild(simgear::PropertyList::iterator child);

  /**
   * Protected constructor for making new nodes on demand.
   */
  SGPropertyNode (const std::string& name, int index, SGPropertyNode * parent);
  template<typename Itr>
  SGPropertyNode (Itr begin, Itr end, int index, SGPropertyNode * parent);

  static simgear::PropertyInterpolationMgr* _interpolation_mgr;

private:

  // Get the raw value
  bool get_bool () const;
  int get_int () const;
  long get_long () const;
  float get_float () const;
  double get_double () const;
  const char * get_string () const;

  // Set the raw value
  bool set_bool (bool value);
  bool set_int (int value);
  bool set_long (long value);
  bool set_float (float value);
  bool set_double (double value);
  bool set_string (const char * value);


  /**
   * Get the value as a string.
   */
  const char * make_string () const;

  /**
   * Trace a read access.
   */
  void trace_read () const;


  /**
   * Trace a write access.
   */
  void trace_write () const;

  int _index;
  std::string _name;
  /// To avoid cyclic reference counting loops this shall not be a reference
  /// counted pointer
  SGPropertyNode * _parent;
  simgear::PropertyList _children;
  mutable std::string _buffer;
  simgear::props::Type _type;
  bool _tied;
  int _attr;

  // The right kind of pointer...
  union {
    SGPropertyNode * alias;
    SGRaw* val;
  } _value;

  union {
    bool bool_val;
    int int_val;
    long long_val;
    float float_val;
    double double_val;
    char * string_val;
  } _local_val;

  std::vector<SGPropertyChangeListener *> * _listeners;

  // Pass name as a pair of iterators
  template<typename Itr>
  SGPropertyNode * getChildImpl (Itr begin, Itr end, int index = 0, bool create = false);
  // very internal method
  template<typename Itr>
  SGPropertyNode* getExistingChild (Itr begin, Itr end, int index);
  // very internal path parsing function
  template<typename SplitItr>
  friend SGPropertyNode* find_node_aux(SGPropertyNode * current, SplitItr& itr,
                                       bool create, int last_index);
  // For boost
  friend size_t hash_value(const SGPropertyNode& node);
};

// Convenience functions for use in templates
template<typename T>
typename boost::disable_if<boost::is_enum<T>, T>::type
getValue(const SGPropertyNode*);

template<>
inline bool getValue<bool>(const SGPropertyNode* node) { return node->getBoolValue(); }

template<>
inline int getValue<int>(const SGPropertyNode* node) { return node->getIntValue(); }

template<>
inline long getValue<long>(const SGPropertyNode* node) { return node->getLongValue(); }

template<>
inline float getValue<float>(const SGPropertyNode* node)
{
    return node->getFloatValue();
}

template<>
inline double getValue<double>(const SGPropertyNode* node)
{
    return node->getDoubleValue();
}

template<>
inline const char * getValue<const char*>(const SGPropertyNode* node)
{
    return node->getStringValue ();
}

template<>
inline std::string getValue<std::string>(const SGPropertyNode* node)
{
    return node->getStringValue();
}

namespace simgear
{
  /**
   * Default trait for extracting enum values from SGPropertyNode. Create your
   * own specialization for specific enum types to enable validation of values.
   */
  template<class T>
  struct enum_traits
  {
    /**
     * Typename of the enum
     */
    static const char* name() { return typeid(T).name(); }

    /**
     * @return Default value (will be used if validation fails)
     */
    static T defVal() { return T(); }

    /**
     * @return Whether the given integer value has an enum value defined
     */
    static bool validate(int) { return true; }
  };
} // namespace simgear

/** Extract enum from SGPropertyNode */
template<typename T>
inline typename boost::enable_if<boost::is_enum<T>, T>::type
getValue(const SGPropertyNode* node)
{
  typedef simgear::enum_traits<T> Traits;
  int val = node->getIntValue();
  if( !Traits::validate(val) )
  {
    SG_LOG
    (
      SG_GENERAL,
      SG_WARN,
      "Invalid value for enum (" << Traits::name() << ", val = " << val << ")"
    );
    return Traits::defVal();
  }
  return static_cast<T>(node->getIntValue());
}

inline bool setValue(SGPropertyNode* node, bool value)
{
    return node->setBoolValue(value);
}

inline bool setValue(SGPropertyNode* node, int value)
{
    return node->setIntValue(value);
}

inline bool setValue(SGPropertyNode* node, long value)
{
    return node->setLongValue(value);
}

inline bool setValue(SGPropertyNode* node, float value)
{
    return node->setFloatValue(value);
}

inline bool setValue(SGPropertyNode* node, double value)
{
    return node->setDoubleValue(value);
}

inline bool setValue(SGPropertyNode* node, const char* value)
{
    return node->setStringValue(value);
}

inline bool setValue (SGPropertyNode* node, const std::string& value)
{
    return node->setStringValue(value.c_str());
}

template<typename T>
bool SGPropertyNode::tie(const SGRawValue<T> &rawValue, bool useDefault)
{
    using namespace simgear::props;
    if (_type == ALIAS || _tied)
        return false;

    useDefault = useDefault && hasValue();
    T old_val = SGRawValue<T>::DefaultValue();
    if (useDefault)
        old_val = getValue<T>(this);
    clearValue();
    if (PropertyTraits<T>::Internal)
        _type = PropertyTraits<T>::type_tag;
    else
        _type = EXTENDED;
    _tied = true;
    _value.val = rawValue.clone();
    if (useDefault) {
        int save_attributes = getAttributes();
        setAttribute( WRITE, true );
        setValue(old_val);
        setAttributes( save_attributes );
    }
    return true;
}

template<>
bool SGPropertyNode::tie (const SGRawValue<const char *> &rawValue,
                          bool useDefault);

template<typename T>
T SGPropertyNode::getValue(typename boost::disable_if_c<simgear::props
                           ::PropertyTraits<T>::Internal>::type* dummy) const
{
    using namespace simgear::props;
    if (_attr == (READ|WRITE) && _type == EXTENDED
        && _value.val->getType() == PropertyTraits<T>::type_tag) {
        return static_cast<SGRawValue<T>*>(_value.val)->getValue();
    }
    if (getAttribute(TRACE_READ))
        trace_read();
    if (!getAttribute(READ))
      return SGRawValue<T>::DefaultValue();
    switch (_type) {
    case EXTENDED:
        if (_value.val->getType() == PropertyTraits<T>::type_tag)
            return static_cast<SGRawValue<T>*>(_value.val)->getValue();
        break;
    case STRING:
    case UNSPECIFIED:
        return simgear::parseString<T>(make_string());
        break;
    default: // avoid compiler warning
        break;
    }
    return SGRawValue<T>::DefaultValue();
}

template<typename T>
inline T SGPropertyNode::getValue(typename boost::enable_if_c<simgear::props
                                  ::PropertyTraits<T>::Internal>::type* dummy) const
{
  return ::getValue<T>(this);
}

template<typename T, typename T_get /* = T */> // TODO use C++11 or traits
std::vector<T> SGPropertyNode::getChildValues(const std::string& name) const
{
  const simgear::PropertyList& props = getChildren(name);
  std::vector<T> values( props.size() );

  for( size_t i = 0; i < props.size(); ++i )
    values[i] = props[i]->getValue<T_get>();

  return values;
}

template<typename T>
inline
std::vector<T> SGPropertyNode::getChildValues(const std::string& name) const
{
  return getChildValues<T, T>(name);
}

template<typename T>
bool SGPropertyNode::setValue(const T& val,
                              typename boost::disable_if_c<simgear::props
                              ::PropertyTraits<T>::Internal>::type* dummy)
{
    using namespace simgear::props;
    if (_attr == (READ|WRITE) && _type == EXTENDED
        && _value.val->getType() == PropertyTraits<T>::type_tag) {
        static_cast<SGRawValue<T>*>(_value.val)->setValue(val);
        return true;
    }
    if (getAttribute(WRITE)
        && ((_type == EXTENDED
            && _value.val->getType() == PropertyTraits<T>::type_tag)
            || _type == NONE || _type == UNSPECIFIED)) {
        if (_type == NONE || _type == UNSPECIFIED) {
            clearValue();
            _type = EXTENDED;
            _value.val = new SGRawValueContainer<T>(val);
        } else {
            static_cast<SGRawValue<T>*>(_value.val)->setValue(val);
        }
        if (getAttribute(TRACE_WRITE))
            trace_write();
        return true;
    }
    return false;
}

template<typename T>
inline bool SGPropertyNode::setValue(const T& val,
                                     typename boost::enable_if_c<simgear::props
                                     ::PropertyTraits<T>::Internal>::type* dummy)
{
  return ::setValue(this, val);
}

/**
 * Utility function for creation of a child property node.
 */
inline SGPropertyNode* makeChild(SGPropertyNode* parent, const char* name,
                                 int index = 0)
{
    return parent->getChild(name, index, true);
}

/**
 * Utility function for creation of a child property node using a
 * relative path.
 */
namespace simgear
{
template<typename StringType>
inline SGPropertyNode* makeNode(SGPropertyNode* parent, const StringType& name)
{
    return parent->getNode(name, true);
}
}

// For boost::hash
size_t hash_value(const SGPropertyNode& node);

// Helper comparison and hash functions for common cases

namespace simgear
{
namespace props
{
struct Compare
{
    bool operator()(const SGPropertyNode* lhs, const SGPropertyNode* rhs) const
    {
        return SGPropertyNode::compare(*lhs, *rhs);
    }
    bool operator()(SGPropertyNode_ptr lhs, const SGPropertyNode* rhs) const
    {
        return SGPropertyNode::compare(*lhs, *rhs);
    }
    bool operator()(const SGPropertyNode* lhs, SGPropertyNode_ptr rhs) const
    {
        return SGPropertyNode::compare(*lhs, *rhs);
    }
    bool operator()(SGPropertyNode_ptr lhs, SGPropertyNode_ptr rhs) const
    {
        return SGPropertyNode::compare(*lhs, *rhs);
    }
};

struct Hash
{
    size_t operator()(const SGPropertyNode* node) const
    {
        return hash_value(*node);
    }
    size_t operator()(SGPropertyNode_ptr node) const
    {
        return hash_value(*node);
    }
};
}
}

/** Convenience class for change listener callbacks without
 * creating a derived class implementing a "valueChanged" method.
 * Also removes listener on destruction automatically.
 */
template<class T>
class SGPropertyChangeCallback
    : public SGPropertyChangeListener
{
public:
    SGPropertyChangeCallback(T* obj, void (T::*method)(SGPropertyNode*),
                             SGPropertyNode_ptr property,bool initial=false)
        : _obj(obj), _callback(method), _property(property)
    {
        _property->addChangeListener(this,initial);
    }

	SGPropertyChangeCallback(const SGPropertyChangeCallback<T>& other) :
		_obj(other._obj), _callback(other._callback), _property(other._property)
	{
		 _property->addChangeListener(this,false);
	}

    virtual ~SGPropertyChangeCallback()
    {
        _property->removeChangeListener(this);
    }
    void valueChanged (SGPropertyNode * node)
    {
        (_obj->*_callback)(node);
    }
private:
    T* _obj;
    void (T::*_callback)(SGPropertyNode*);
    SGPropertyNode_ptr _property;
};

#endif // __PROPS_HXX

// end of props.hxx