/usr/share/doc/swi-prolog-doc/UserGuide/slots.html

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<H2><A NAME="sec:7.2"><SPAN class="sec-nr">7.2</SPAN> <SPAN class="sec-title">Accessing 
instance variables (slots)</SPAN></A></H2>

<A NAME="sec:slots"></A>

<P>The method <A NAME="idx:objectbothslot:203"></A>`<B>object<CODE>&lt;-&gt;</CODE>slot</B>' 
is used to access slots directly, bypassing possible methods with the 
same name. Normally, it should only be used in
<B><CODE>-&gt;</CODE>initialise</B> (see below) and when defining a 
method with the same name as a variable. Below is a fragment where a <TT>type</TT> 
slot is displayed by a text object named <TT>type</TT> in a graphical 
object. This variable has access <TT>get</TT>, associating a universal 
method <B><CODE>&lt;-</CODE>type</B> that yields the current value of 
the slot. The implementation of <B><CODE>-&gt;</CODE>type</B> uses the
<B><CODE>-&gt;</CODE>slot</B> method to write the argument in the <B><CODE>&lt;-</CODE>type</B> 
slot and subsequently performs the required side-effects. The ... 
indicate where the fragment is incomplete.

<PRE class="code">
variable(type,  name,   get, "Epistemological type").

initialise(D, Type:name, ...) :-&gt;
        send_super(D, initialise),
        send(D, slot, type, Type),
        send(D, display, new(T, text(Type))),
        send(T, name, type),
        ...

type(D, Type:type) :-&gt;
        "Modify the epistemological type"::
        send(D, slot, type, Type),
        get(D, member, type, Text),
        send(Text, string, Type).
</PRE>

<DL>
<DT><STRONG>object -&gt;slot:</STRONG> <VAR>name, unchecked</VAR></DT>
<DD class="defbody">
</DD>
<DT><STRONG>object &lt;-slot:</STRONG> <VAR>name</VAR></DT>
<DD class="defbody">
uncheckedRead or write slot without side-effects. The value will be 
converted to the type of the instance variable addressed. An error is 
raised if this conversion is not defined or if the slot does not exist.
</DD>
</DL>

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swi-prolog-doc 5.6.59-2 / usr / share / doc / swi-prolog-doc / UserGuide / slots.html
