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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).
- ]
- [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]
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