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<H2><A NAME="sec:E.3"><SPAN class="sec-nr">E.3</SPAN> <SPAN class="sec-title">Memory
usage of objects</SPAN></A></H2>
<P><A NAME="idx:objectmemoryusage:726"></A><A NAME="idx:memoryusage:727"></A>Currently
an object consists of an object-header and an array of instance
variables. The object-header includes various flags, a reference count
and a pointer to the class. The size of an object header is 12 bytes.
Each instance variable consumes an additional 4 bytes. For example a
point object has `x' and `y' instance variables and thus consumes <VAR>12
+ 2 * 4 = 20</VAR> bytes.
<P>The method <A NAME="idx:classgetinstancesize:728"></A>`<B>class<CODE><-</CODE>instance_size</B>'
returns the size of an instance of this class in bytes. Note that the
costs of supporting objects is not considered in this value. For example
a box object has instance size:
<PRE class="code">
1 ?- get(class(box), instance_size, S).
S = 72
</PRE>
<P>But a box has an <B><CODE><-</CODE>area</B> instance variable
consuming an additional 28 bytes.
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