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## Macro BOOST_TYPE_ERASURE_FREE

BOOST_TYPE_ERASURE_FREE — Defines a primitive concept for a free function.

## Synopsis

    // In header: <boost/type_erasure/free.hpp>

    BOOST_TYPE_ERASURE_FREE(concept_name, function_name)

## Description

The declaration of the concept is

    template<class Sig>
    struct concept_name;

where Sig is a function type giving the signature of the function.

This macro can only be used at namespace scope.

Example:

    BOOST_TYPE_ERASURE_FREE(to_string)
    typedef has_to_string<std::string(_self const&)> to_string_concept;

In C++03, the macro can only be used in the global namespace and is defined as:

    #define BOOST_TYPE_ERASURE_FREE(qualified_name, function_name, N)

Example:

    BOOST_TYPE_ERASURE_FREE((boost)(has_to_string), to_string, 1)

For backwards compatibility, this form is always accepted.

Parameters: |
`concept_name` | is the name of the concept to declare. If it is omitted it defaults to `has_ ## function_name`
`function_name` | is the name of the function.