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#### is_file

Determine if `T` meets the requirements of File.

##### Synopsis

Defined in header `<boost/beast/core/file_base.hpp>`

    template<
        class T>
    struct is_file :
        public std::integral_constant< bool,... >

##### Description

Metafunctions are used to perform compile time checking of template types. This type will be `std::true_type` if `T` meets the requirements, else the type will be `std::false_type`.

##### Example

Use with `static_assert`:

    template < class File>
    void f(File& file)
    {
        static_assert (is_file<File>::value,
            "File type requirements not met" );
    ...

Use with `std::enable_if` (SFINAE):

    template < class File>
    typename std::enable_if<is_file<File>::value>::type
    f(File& file);