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<Head>
<Title>Predicate</Title>
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<H1>Predicate</H1>
<Table CellPadding=0 CellSpacing=0 width=100%>
<TR>
<TD Align=left><Img src = "functors.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>: functors</TD>
<TD Align=right VAlign=top><b>Component type</b>: concept</TD>
</TR>
</Table>
<h3>Description</h3>
A Predicate is a <A href="UnaryFunction.html">Unary Function</A> whose result represents the truth or
falsehood of some condition. A Predicate might, for example, be a
function that takes an argument of type <tt>int</tt> and returns <tt>true</tt> if the
argument is positive.
<h3>Refinement of</h3>
<A href="UnaryFunction.html">Unary Function</A>
<h3>Associated types</h3>
<Table border>
<TR>
<TD VAlign=top>
Result type
</TD>
<TD VAlign=top>
The type returned when the Predicate is called. The result type
must be convertible to <tt>bool</tt>.
</TD>
</tr>
</table>
<h3>Notation</h3>
<Table>
<TR>
<TD VAlign=top>
<tt>F</tt>
</TD>
<TD VAlign=top>
A type that is a model of Predicate
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>X</tt>
</TD>
<TD VAlign=top>
The argument type of <tt>F</tt>
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>f</tt>
</TD>
<TD VAlign=top>
Object of type <tt>F</tt>
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>x</tt>
</TD>
<TD VAlign=top>
Object of type <tt>X</tt>
</TD>
</tr>
</table>
<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>
Function call
</TD>
<TD VAlign=top>
<tt>f(x)</tt>
</TD>
<TD VAlign=top>
</TD>
<TD VAlign=top>
Convertible to <tt>bool</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>
Function call
</TD>
<TD VAlign=top>
<tt>f(x)</tt>
</TD>
<TD VAlign=top>
<tt>x</tt> is in the domain of <tt>f</tt>.
</TD>
<TD VAlign=top>
Returns <tt>true</tt> if the condition is satisfied, <tt>false</tt> if it is not.
</TD>
<TD VAlign=top>
The result is either <tt>true</tt> or <tt>false</tt>.
</TD>
</tr>
</table>
<h3>Complexity guarantees</h3>
<h3>Invariants</h3>
<h3>Models</h3>
<UL>
<LI>
<tt>bool (*)(int)</tt>
</UL>
<h3>Notes</h3>
<h3>See also</h3>
<A href="AdaptablePredicate.html">Adaptable Predicate</A>, <A href="BinaryPredicate.html">Binary Predicate</A>, <A href="AdaptableBinaryPredicate.html">Adaptable Binary Predicate</A>
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