boost::gil::make_reader

template<
    typename String,
    typename FormatTag,
    typename ConversionPolicy>
get_reader<String, FormatTag, ConversionPolicy>::type
make_reader(
    String const& file_name,
    FormatTag const&,
    ConversionPolicy const& cc)
requires mp11::mp_and
        <
            detail::is_supported_path_spec<String>,
            is_format_tag<FormatTag>
        >::value;