/usr/share/doc/stl-manual/html/Assignable.html

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<Title>Assignable</Title>
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<H1>Assignable</H1>

<Table CellPadding=0 CellSpacing=0 width=100%>
<TR>
<TD Align=left><Img src = "utilities.gif" Alt=""   WIDTH = "194"  HEIGHT = "38" ></TD>
<TD Align=right><Img src = "concept.gif" Alt=""   WIDTH = "194"  HEIGHT = "38" ></TD>
</TR>
<TR>
<TD Align=left VAlign=top><b>Category</b>: utilities</TD>
<TD Align=right VAlign=top><b>Component type</b>: concept</TD>
</TR>
</Table>

<h3>Description</h3>
A type is Assignable if it is possible to copy objects of that type and
to assign values to variables.
<h3>Refinement of</h3>
<h3>Associated types</h3>
<h3>Notation</h3>
<Table>
<TR>
<TD VAlign=top>
<tt>X</tt>
</TD>
<TD VAlign=top>
A type that is a model of Assignable
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>x</tt>, <tt>y</tt>
</TD>
<TD VAlign=top>
Object of type <tt>X</tt>
</TD>
</tr>
</table>
<h3>Definitions</h3>
<h3>Valid expressions</h3>
<Table border>
<TR>
<TH>
Name
</TH>
<TH>
Expression
</TH>
<TH>
Type requirements
</TH>
<TH>
Return type
</TH>
</TR>
<TR>
<TD VAlign=top>
Copy constructor
</TD>
<TD VAlign=top>
<tt>X(x)</tt>
</TD>
<TD VAlign=top>
&nbsp;
</TD>
<TD VAlign=top>
<tt>X</tt>
</TD>
</TR>
<TR>
<TD VAlign=top>
Copy constructor
</TD>
<TD VAlign=top>
<pre>
X x(y);
X x = y;
</pre>
</TD>
<TD VAlign=top>
&nbsp;
</TD>
<TD VAlign=top>
&nbsp;
</TD>
</TR>
<TR>
<TD VAlign=top>
Assignment
</TD>
<TD VAlign=top>
<tt>x = y</tt> <A href="#1">[1]</A>
</TD>
<TD VAlign=top>
&nbsp;
</TD>
<TD VAlign=top>
<tt>X&amp;</tt>
</TD>
</TR>
<TR>
<TD VAlign=top>
Swap
</TD>
<TD VAlign=top>
<tt>swap(x,y)</tt>
</TD>
<TD VAlign=top>
&nbsp;
</TD>
<TD VAlign=top>
<tt>void</tt>
</TD>
</tr>
</table>
<h3>Expression semantics</h3>
<Table border>
<TR>
<TH>
Name
</TH>
<TH>
Expression
</TH>
<TH>
Precondition
</TH>
<TH>
Semantics
</TH>
<TH>
Postcondition
</TH>
</TR>
<TR>
<TD VAlign=top>
Copy constructor
</TD>
<TD VAlign=top>
<tt>X(x)</tt>
</TD>
<TD VAlign=top>
&nbsp;
</TD>
<TD VAlign=top>
&nbsp;
</TD>
<TD VAlign=top>
<tt>X(x)</tt> is a copy of <tt>x</tt> <A href="#2">[2]</A>
</TD>
</TR>
<TR>
<TD VAlign=top>
Copy constructor
</TD>
<TD VAlign=top>
<tt>X(x)</tt>
</TD>
<TD VAlign=top>
&nbsp;
</TD>
<TD VAlign=top>
&nbsp;
</TD>
<TD VAlign=top>
<tt>X(x)</tt> is a copy of <tt>x</tt> <A href="#2">[2]</A>
</TD>
</TR>
<TR>
<TD VAlign=top>
Copy constructor
</TD>
<TD VAlign=top>
<pre>
X x(y);
X x = y;
</pre>
</TD>
<TD VAlign=top>
&nbsp;
</TD>
<TD VAlign=top>
&nbsp;
</TD>
<TD VAlign=top>
<tt>x</tt> is a copy of <tt>y</tt> <A href="#2">[2]</A>
</TD>
</TR>
<TR>
<TD VAlign=top>
Assignment
</TD>
<TD VAlign=top>
<tt>x</tt> = <tt>y</tt> <A href="#1">[1]</A>
</TD>
<TD VAlign=top>
&nbsp;
</TD>
<TD VAlign=top>
&nbsp;
</TD>
<TD VAlign=top>
<tt>x</tt> is a copy of <tt>y</tt> <A href="#2">[2]</A>
</TD>
</TR>
<TR>
<TD VAlign=top>
Swap
</TD>
<TD VAlign=top>
<tt><A href="swap.html">swap</A>(x,y)</tt>
</TD>
<TD VAlign=top>
&nbsp;
</TD>
<TD VAlign=top>
Equivalent to
<pre>
{
  X tmp = x; 
  x = y; 
  y = tmp; 
}
</pre>
</TD>
<TD VAlign=top>
&nbsp;
</TD>
</tr>
</table>
<h3>Complexity guarantees</h3>
<h3>Invariants</h3>
<h3>Models</h3>
<UL>
<LI>
int
</UL>
<h3>Notes</h3>
<P><A name="1">[1]</A>
One implication of this requirement is that a <tt>const</tt> type is not Assignable.
For example, <tt>const int</tt> is not Assignable: if <tt>x</tt> is declared to be
of type <tt>const int</tt>, then <tt>x = 7</tt> is illegal.  Similarly, the type
<tt><A href="pair.html">pair</A>&lt;const int, int&gt;</tt> is not Assignable.
<P><A name="2">[2]</A>
The reason this says &quot;<tt>x</tt> is a copy of <tt>y</tt>&quot;, rather than
&quot;<tt>x == y</tt>&quot;, is that <tt>operator==</tt> is not necessarily defined: equality
is not a requirement of Assignable.  If the type <tt>X</tt> is
<A href="EqualityComparable.html">EqualityComparable</A> as well as Assignable, then a copy of <tt>x</tt> 
should compare equal to <tt>x</tt>.
<h3>See also</h3>
<A href="DefaultConstructible.html">DefaultConstructible</A>

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stl-manual 3.30-13 / usr / share / doc / stl-manual / html / Assignable.html
