libcapnp-dev 0.4.0-1ubuntu2 / usr / include / kj / tuple.h

// Copyright (c) 2013, Kenton Varda <temporal@gmail.com>
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this
//    list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright notice,
//    this list of conditions and the following disclaimer in the documentation
//    and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
// ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
// ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// This file defines a notion of tuples that is simpler that `std::tuple`.  It works as follows:
// - `kj::Tuple<A, B, C> is the type of a tuple of an A, a B, and a C.
// - `kj::tuple(a, b, c)` returns a tuple containing a, b, and c.  If any of these are themselves
//   tuples, they are flattened, so `tuple(a, tuple(b, c), d)` is equivalent to `tuple(a, b, c, d)`.
// - `kj::get<n>(myTuple)` returns the element of `myTuple` at index n.
// - `kj::apply(func, ...)` calls func on the following arguments after first expanding any tuples
//   in the argument list.  So `kj::apply(foo, a, tuple(b, c), d)` would call `foo(a, b, c, d)`.
//
// Note that:
// - The type `Tuple<T>` is a synonym for T.  This is why `get` and `apply` are not members of the
//   type.
// - It is illegal for an element of `Tuple` to itself be a tuple, as tuples are meant to be
//   flattened.
// - It is illegal for an element of `Tuple` to be a reference, due to problems this would cause
//   with type inference and `tuple()`.

#ifndef KJ_TUPLE_H_
#define KJ_TUPLE_H_

#include "common.h"

namespace kj {
namespace _ {  // private

template <size_t index, typename... T>
struct TypeByIndex_;
template <typename First, typename... Rest>
struct TypeByIndex_<0, First, Rest...> {
  typedef First Type;
};
template <size_t index, typename First, typename... Rest>
struct TypeByIndex_<index, First, Rest...>
    : public TypeByIndex_<index - 1, Rest...> {};
template <size_t index>
struct TypeByIndex_<index> {
  static_assert(index != index, "Index out-of-range.");
};
template <size_t index, typename... T>
using TypeByIndex = typename TypeByIndex_<index, T...>::Type;
// Chose a particular type out of a list of types, by index.

template <size_t... s>
struct Indexes {};
// Dummy helper type that just encapsulates a sequential list of indexes, so that we can match
// templates against them and unpack them with '...'.

template <size_t end, size_t... prefix>
struct MakeIndexes_: public MakeIndexes_<end - 1, end - 1, prefix...> {};
template <size_t... prefix>
struct MakeIndexes_<0, prefix...> {
  typedef Indexes<prefix...> Type;
};
template <size_t end>
using MakeIndexes = typename MakeIndexes_<end>::Type;
// Equivalent to Indexes<0, 1, 2, ..., end>.

template <typename... T>
class Tuple;
template <size_t index, typename... U>
inline TypeByIndex<index, U...>& getImpl(Tuple<U...>& tuple);
template <size_t index, typename... U>
inline TypeByIndex<index, U...>&& getImpl(Tuple<U...>&& tuple);
template <size_t index, typename... U>
inline const TypeByIndex<index, U...>& getImpl(const Tuple<U...>& tuple);

template <uint index, typename T>
struct TupleElement {
  // Encapsulates one element of a tuple.  The actual tuple implementation multiply-inherits
  // from a TupleElement for each element, which is more efficient than a recursive definition.

  T value;
  TupleElement() = default;
  constexpr inline TupleElement(const T& value): value(value) {}
  constexpr inline TupleElement(T&& value): value(kj::mv(value)) {}
};

template <uint index, typename T>
struct TupleElement<index, T&> {
  // If tuples contained references, one of the following would have to be true:
  // - `auto x = tuple(y, z)` would cause x to be a tuple of references to y and z, which is
  //   probably not what you expected.
  // - `Tuple<Foo&, Bar&> x = tuple(a, b)` would not work, because `tuple()` returned
  //   Tuple<Foo, Bar>.
  static_assert(sizeof(T*) == 0, "Sorry, tuples cannot contain references.");
};

template <uint index, typename... T>
struct TupleElement<index, Tuple<T...>> {
  static_assert(sizeof(Tuple<T...>*) == 0,
                "Tuples cannot contain other tuples -- they should be flattened.");
};

template <typename Indexes, typename... Types>
struct TupleImpl;

template <size_t... indexes, typename... Types>
struct TupleImpl<Indexes<indexes...>, Types...>
    : public TupleElement<indexes, Types>... {
  // Implementation of Tuple.  The only reason we need this rather than rolling this into class
  // Tuple (below) is so that we can get "indexes" as an unpackable list.

  static_assert(sizeof...(indexes) == sizeof...(Types), "Incorrect use of TupleImpl.");

  template <typename... Params>
  inline TupleImpl(Params&&... params)
      : TupleElement<indexes, Types>(kj::fwd<Params>(params))... {
    // Work around Clang 3.2 bug 16303 where this is not detected.  (Unfortunately, Clang sometimes
    // segfaults instead.)
    static_assert(sizeof...(params) == sizeof...(indexes),
                  "Wrong number of parameters to Tuple constructor.");
  }

  template <typename... U>
  constexpr inline TupleImpl(Tuple<U...>&& other)
      : TupleElement<indexes, Types>(kj::mv(getImpl<indexes>(other)))... {}
  template <typename... U>
  constexpr inline TupleImpl(Tuple<U...>& other)
      : TupleElement<indexes, Types>(getImpl<indexes>(other))... {}
  template <typename... U>
  constexpr inline TupleImpl(const Tuple<U...>& other)
      : TupleElement<indexes, Types>(getImpl<indexes>(other))... {}
};

struct MakeTupleFunc;

template <typename... T>
class Tuple {
  // The actual Tuple class (used for tuples of size other than 1).

public:
  Tuple() = default;
  template <typename... U>
  constexpr inline Tuple(Tuple<U...>&& other): impl(kj::mv(other)) {}
  template <typename... U>
  constexpr inline Tuple(Tuple<U...>& other): impl(other) {}
  template <typename... U>
  constexpr inline Tuple(const Tuple<U...>& other): impl(other) {}

private:
  template <typename... Params>
  constexpr Tuple(Params&&... params): impl(kj::fwd<Params>(params)...) {}

  TupleImpl<MakeIndexes<sizeof...(T)>, T...> impl;

  template <size_t index, typename... U>
  friend inline TypeByIndex<index, U...>& getImpl(Tuple<U...>& tuple);
  template <size_t index, typename... U>
  friend inline TypeByIndex<index, U...>&& getImpl(Tuple<U...>&& tuple);
  template <size_t index, typename... U>
  friend inline const TypeByIndex<index, U...>& getImpl(const Tuple<U...>& tuple);
  friend struct MakeTupleFunc;
};

template <>
class Tuple<> {
  // Simplified zero-member version of Tuple.  In particular this is important to make sure that
  // Tuple<>() is constexpr.
};

template <typename T>
class Tuple<T>;
// Single-element tuple should never be used.  The public API should ensure this.

template <size_t index, typename... T>
inline TypeByIndex<index, T...>& getImpl(Tuple<T...>& tuple) {
  // Get member of a Tuple by index, e.g. `get<2>(myTuple)`.
  static_assert(index < sizeof...(T), "Tuple element index out-of-bounds.");
  return implicitCast<TupleElement<index, TypeByIndex<index, T...>>&>(tuple.impl).value;
}
template <size_t index, typename... T>
inline TypeByIndex<index, T...>&& getImpl(Tuple<T...>&& tuple) {
  // Get member of a Tuple by index, e.g. `get<2>(myTuple)`.
  static_assert(index < sizeof...(T), "Tuple element index out-of-bounds.");
  return kj::mv(implicitCast<TupleElement<index, TypeByIndex<index, T...>>&>(tuple.impl).value);
}
template <size_t index, typename... T>
inline const TypeByIndex<index, T...>& getImpl(const Tuple<T...>& tuple) {
  // Get member of a Tuple by index, e.g. `get<2>(myTuple)`.
  static_assert(index < sizeof...(T), "Tuple element index out-of-bounds.");
  return implicitCast<const TupleElement<index, TypeByIndex<index, T...>>&>(tuple.impl).value;
}
template <size_t index, typename T>
inline T&& getImpl(T&& value) {
  // Get member of a Tuple by index, e.g. `getImpl<2>(myTuple)`.

  // Non-tuples are equivalent to one-element tuples.
  static_assert(index == 0, "Tuple element index out-of-bounds.");
  return kj::fwd<T>(value);
}


template <typename Func, typename SoFar, typename... T>
struct ExpandAndApplyResult_;
// Template which computes the return type of applying Func to T... after flattening tuples.
// SoFar starts as Tuple<> and accumulates the flattened parameter types -- so after this template
// is recursively expanded, T... is empty and SoFar is a Tuple containing all the parameters.

template <typename Func, typename First, typename... Rest, typename... T>
struct ExpandAndApplyResult_<Func, Tuple<T...>, First, Rest...>
    : public ExpandAndApplyResult_<Func, Tuple<T..., First>, Rest...> {};
template <typename Func, typename... FirstTypes, typename... Rest, typename... T>
struct ExpandAndApplyResult_<Func, Tuple<T...>, Tuple<FirstTypes...>, Rest...>
    : public ExpandAndApplyResult_<Func, Tuple<T...>, FirstTypes&&..., Rest...> {};
template <typename Func, typename... FirstTypes, typename... Rest, typename... T>
struct ExpandAndApplyResult_<Func, Tuple<T...>, Tuple<FirstTypes...>&, Rest...>
    : public ExpandAndApplyResult_<Func, Tuple<T...>, FirstTypes&..., Rest...> {};
template <typename Func, typename... FirstTypes, typename... Rest, typename... T>
struct ExpandAndApplyResult_<Func, Tuple<T...>, const Tuple<FirstTypes...>&, Rest...>
    : public ExpandAndApplyResult_<Func, Tuple<T...>, const FirstTypes&..., Rest...> {};
template <typename Func, typename... T>
struct ExpandAndApplyResult_<Func, Tuple<T...>> {
  typedef decltype(instance<Func>()(instance<T&&>()...)) Type;
};
template <typename Func, typename... T>
using ExpandAndApplyResult = typename ExpandAndApplyResult_<Func, Tuple<>, T...>::Type;
// Computes the expected return type of `expandAndApply()`.

template <typename Func>
inline auto expandAndApply(Func&& func) -> ExpandAndApplyResult<Func> {
  return func();
}

template <typename Func, typename First, typename... Rest>
struct ExpandAndApplyFunc {
  Func&& func;
  First&& first;
  ExpandAndApplyFunc(Func&& func, First&& first)
      : func(kj::fwd<Func>(func)), first(kj::fwd<First>(first)) {}
  template <typename... T>
  auto operator()(T&&... params)
      -> decltype(this->func(kj::fwd<First>(first), kj::fwd<T>(params)...)) {
    return this->func(kj::fwd<First>(first), kj::fwd<T>(params)...);
  }
};

template <typename Func, typename First, typename... Rest>
inline auto expandAndApply(Func&& func, First&& first, Rest&&... rest)
    -> ExpandAndApplyResult<Func, First, Rest...> {

  return expandAndApply(
      ExpandAndApplyFunc<Func, First, Rest...>(kj::fwd<Func>(func), kj::fwd<First>(first)),
      kj::fwd<Rest>(rest)...);
}

template <typename Func, typename... FirstTypes, typename... Rest>
inline auto expandAndApply(Func&& func, Tuple<FirstTypes...>&& first, Rest&&... rest)
    -> ExpandAndApplyResult<Func, FirstTypes&&..., Rest...> {
  return expandAndApplyWithIndexes(MakeIndexes<sizeof...(FirstTypes)>(),
      kj::fwd<Func>(func), kj::mv(first), kj::fwd<Rest>(rest)...);
}

template <typename Func, typename... FirstTypes, typename... Rest>
inline auto expandAndApply(Func&& func, Tuple<FirstTypes...>& first, Rest&&... rest)
    -> ExpandAndApplyResult<Func, FirstTypes..., Rest...> {
  return expandAndApplyWithIndexes(MakeIndexes<sizeof...(FirstTypes)>(),
      kj::fwd<Func>(func), first, kj::fwd<Rest>(rest)...);
}

template <typename Func, typename... FirstTypes, typename... Rest>
inline auto expandAndApply(Func&& func, const Tuple<FirstTypes...>& first, Rest&&... rest)
    -> ExpandAndApplyResult<Func, FirstTypes..., Rest...> {
  return expandAndApplyWithIndexes(MakeIndexes<sizeof...(FirstTypes)>(),
      kj::fwd<Func>(func), first, kj::fwd<Rest>(rest)...);
}

template <typename Func, typename... FirstTypes, typename... Rest, size_t... indexes>
inline auto expandAndApplyWithIndexes(
    Indexes<indexes...>, Func&& func, Tuple<FirstTypes...>&& first, Rest&&... rest)
    -> ExpandAndApplyResult<Func, FirstTypes&&..., Rest...> {
  return expandAndApply(kj::fwd<Func>(func), kj::mv(getImpl<indexes>(first))...,
                        kj::fwd<Rest>(rest)...);
}

template <typename Func, typename... FirstTypes, typename... Rest, size_t... indexes>
inline auto expandAndApplyWithIndexes(
    Indexes<indexes...>, Func&& func, const Tuple<FirstTypes...>& first, Rest&&... rest)
    -> ExpandAndApplyResult<Func, FirstTypes..., Rest...> {
  return expandAndApply(kj::fwd<Func>(func), getImpl<indexes>(first)...,
                       kj::fwd<Rest>(rest)...);
}

struct MakeTupleFunc {
  template <typename... Params>
  Tuple<Decay<Params>...> operator()(Params&&... params) {
    return Tuple<Decay<Params>...>(kj::fwd<Params>(params)...);
  }
  template <typename Param>
  Decay<Param> operator()(Param&& param) {
    return kj::fwd<Param>(param);
  }
};

}  // namespace _ (private)

template <typename... T> struct Tuple_ { typedef _::Tuple<T...> Type; };
template <typename T> struct Tuple_<T> { typedef T Type; };

template <typename... T> using Tuple = typename Tuple_<T...>::Type;
// Tuple type.  `Tuple<T>` (i.e. a single-element tuple) is a synonym for `T`.  Tuples of size
// other than 1 expand to an internal type.  Either way, you can construct a Tuple using
// `kj::tuple(...)`, get an element by index `i` using `kj::get<i>(myTuple)`, and expand the tuple
// as arguments to a function using `kj::apply(func, myTuple)`.
//
// Tuples are always flat -- that is, no element of a Tuple is ever itself a Tuple.  If you
// construct a tuple from other tuples, the elements are flattened and concatenated.

template <typename... Params>
inline auto tuple(Params&&... params)
    -> decltype(_::expandAndApply(_::MakeTupleFunc(), kj::fwd<Params>(params)...)) {
  // Construct a new tuple from the given values.  Any tuples in the argument list will be
  // flattened into the result.
  return _::expandAndApply(_::MakeTupleFunc(), kj::fwd<Params>(params)...);
}

template <size_t index, typename Tuple>
inline auto get(Tuple&& tuple) -> decltype(_::getImpl<index>(kj::fwd<Tuple>(tuple))) {
  // Unpack and return the tuple element at the given index.  The index is specified as a template
  // parameter, e.g. `kj::get<3>(myTuple)`.
  return _::getImpl<index>(kj::fwd<Tuple>(tuple));
}

template <typename Func, typename... Params>
inline auto apply(Func&& func, Params&&... params)
    -> decltype(_::expandAndApply(kj::fwd<Func>(func), kj::fwd<Params>(params)...)) {
  // Apply a function to some arguments, expanding tuples into separate arguments.
  return _::expandAndApply(kj::fwd<Func>(func), kj::fwd<Params>(params)...);
}

}  // namespace kj

#endif  // KJ_TUPLE_H_