forked from boostorg/algorithm
38 lines
4.1 KiB
HTML
38 lines
4.1 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><title> Concepts and External Concepts </title><meta http-equiv="Content-Type"content="text/html; charset=iso-8859-1"></head> <body><table ><tr ><td ><img src="../../../../boost.png" width="100%" border="0"></td><td ><h1 >Concepts and External Concepts</h1></td></tr></table><p >Generic programming in C++ is characterized by the use of function and class templates where
|
|
the template parameter(s) must satisfy certain requirements.Often these
|
|
requirements are so important that we give them a name: we call
|
|
such a set of type requirements a <b>concept</b>. We say that a type <i>
|
|
conforms to a concept</i> or that it <i>is a model of a concept</i> if it
|
|
satisfies all of those requirements. The concept can be specified as a set
|
|
of member functions with well-defined semantics
|
|
and a set of nested typedefs with well-defined properties.</p><p >Often it much more flexible to provide free-standing functions and typedefs
|
|
which provides the exact same semantics (but a different syntax) as
|
|
specified
|
|
by the concept. This allows generic code to treat different types <i> as if
|
|
</i> they fulfilled the concept. In this case we say that the concept has
|
|
been <b> externalized </b> or that the new requirements constitutes an <b>external
|
|
concept </b>. We say that a type <i> conforms to an external concept </i>
|
|
or that it <i> is a model of an external concept </i>. A concept may exist
|
|
without a corresponding external concept and conversely.</p><p >Whenever a concept specifies a member function, the corresponding external
|
|
concept
|
|
must specify a free-standing function of the same name, same return type and
|
|
the same argument list except there is an extra first argument which must
|
|
be of the type (or a reference to that type) that is to fulfill the external
|
|
concept. If the corresonding member function has any cv-qulifiers, the
|
|
first argument must have the same cv-qualifiers. Whenever a concept
|
|
specifies a nested typedef, the corresponding external concept
|
|
specifies a <b>type-generator</b>, that is, a type with a nested typedef
|
|
named <code>type</code>. The type-generator has the name as the nested typedef with
|
|
<code>_of</code> appended.
|
|
The converse relationship of an external concept and its corresponding concept
|
|
also holds.</p><p ><b ><i >Example:</i></b></p><p >A type <code>T</code> fulfills the FooConcept if it
|
|
has the follwing public members:</p><code> void T::foo( int ) const; <br>
|
|
int T::bar(); <br>
|
|
typedef <i>implementation defined </i> foo_type;</code><p >The corresponding external concept is the ExternalFooConcept.</p><p >A type <code>T</code> fullfills the ExternalFooConcept if these
|
|
free-standing functions and type-generators exists:</p><code>void foo( const T&, int ); <br>
|
|
int bar( T& ); <br>
|
|
foo_type_of< T >::type;</code> <br> <br><hr size="1" ><h3 >Literature</h3><ul ><li > <a href="http://www.boost.org/more/generic_programming.html#type_generator" target="_self" >Type Generators</a> </li><li > <a href="http://www.boost.org/more/generic_programming.html#concept" target="_self" >Concepts</a> </li><li > <a href="http://www.sgi.com/tech/stl/stl_introduction.html" target="_self" >Concepts and SGI STL</a> </li></ul><hr size="1" ><p >© Thorsten Ottosen 2003-2004 (nesotto_AT_cs.auc.dk).
|
|
Permission to copy, use, modify, sell and distribute this software is granted provided this copyright notice appears
|
|
in all copies. This software is provided "as is" without express or implied warranty, and with no
|
|
claim as to its suitability for any purpose.</p><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br></body></html>
|
|
<!-- Copyright Dezide Aps 2003-2004 --> |