boost/libs/tti/doc/tti_detail_has_static_member_function.qbk

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  (C) Copyright Edward Diener 2011,2012
  Distributed under the Boost Software License, Version 1.0.
  (See accompanying file LICENSE_1_0.txt or copy at
  http://www.boost.org/LICENSE_1_0.txt).
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[section:tti_detail_has_static_member_function Introspecting static member function]

The TTI macro [macroref BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION] introspects
a static member function of a class.

BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION takes a single
parameter which is the name of an inner static member function whose existence
the programmer wants to check. The macro generates a metafunction
called 'has_static_member_function_'name_of_inner_static_member_function'. 

The metafunction can be invoked in two different ways.

The first way is by passing it the enclosing type to introspect and a 
signature for the static member function as separate template 
arguments. The signature for the static member function consists of a return 
type, optional parameter types in the form of a boost::mpl forward 
sequence of types, and an optional Boost FunctionTypes tag type. A 
typical boost::mpl forward sequence of types is a boost::mpl::vector<>.

The second way is by passing it the enclosing type to introspect and a
signature for the static member function as a function. The function 
has the form of:

 Return_Type ( Parameter_Types )

where the Parameter_Types may be empty, or a comma-separated 
list of parameter types if there are more than one parameter type.

The metafunction returns a single type called 'type', which is a 
boost::mpl::bool_. As a convenience the metafunction 
returns the value of this type directly as a compile time bool constant 
called 'value'. This is true or false depending on whether the inner 
static member function, of the specified signature, exists or not.

[heading Generating the metafunction]

You generate the metafunction by invoking the macro with the name 
of an inner static member function:

  BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION(AStaticMemberFunction)
  
generates a metafunction called 'has_static_member_function_AStaticMemberFunction' in the current scope.

[heading Invoking the metafunction]

You invoke the metafunction by instantiating the template with an enclosing 
type to introspect and the signature of the static member function as a series of template
parameters. Alternatively you can invoke the metafunction by passing it an enclosing type
and the signature of the static member function as a single function type.

A return value called 'value' is a compile time bool constant.

  has_static_member_function_AStaticMemberFunction
    <
    Enclosing_Type,
    StaticMemberFunction_ReturnType,
    boost::mpl::vector<StaticMemberFunction_ParameterTypes>, // optional, can be any mpl forward sequence
    boost::function_types::SomeTagType                       // optional, can be any FunctionTypes tag type
    >::value

  OR  
  
  has_static_member_function_AStaticMemberFunction
    <
    Enclosing_Type,
    Return_Type ( Parameter_Types )
    >::value

[heading Examples]

First we generate metafunctions for various inner static member function names: 

 #include <boost/tti/has_static_member_function.hpp>
 
 BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION(function1)
 BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION(function2)
 BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION(function3)
 
Next let us create some user-defined types we want to introspect. 

 struct AClass { };
 struct Top
   {
   static int function1();
   static AClass function2(double,short *);
   };
 struct Top2
   {
   static long function2(Top &,int,bool,short,float);
   static Top * function3(long,int,AClass &);
   };
   
Finally we invoke our metafunction and return our value.
This all happens at compile time, and can be used by 
programmers doing compile time template metaprogramming.
  
We will show both forms in the following examples. 
Both forms are completely interchangeable as to the result
desired.

 has_static_member_function_function1<Top,int>::value; // true
 has_static_member_function_function1<Top,int ()>::value; // true
 has_static_member_function_function1<Top2,int>::value; // false
 
 has_static_member_function_function2<Top,AClass,boost::mpl::vector<double,short *> >::value; // true
 has_static_member_function_function2<Top2,AClass,boost::mpl::vector<double,short *> >::value; // false
 has_static_member_function_function2<Top2,long (Top &,int,bool,short,float)>::value; // true
 
 has_static_member_function_function3<Top2,int ()>::value; // false
 has_static_member_function_function3<Top2,Top * (long,int,AClass &)>::value; // true;
   
[heading Metafunction re-use]

The macro encodes only the name of the static member function 
for which we are searching and the fact that we are 
introspecting for a static member function within an enclosing type.

Because of this, once we create our metafunction for 
introspecting a static member function by name, we can reuse the 
metafunction for introspecting any enclosing type, having any 
static member function, for that name.

[endsect]