:relfileprefix: ../../../
[#boost-urls-grammar-is_charset]

== xref:boost.adoc[pass:[boost]]::xref:boost/urls.adoc[pass:[urls]]::xref:boost/urls/grammar.adoc[pass:[grammar]]::is_charset


Alias for `std::true_type` if T satisfies
_CharSet_
.


=== Synopsis

Declared in header `<https://www.github.com/boostorg/url/blob/develop/include/boost/url/grammar/charset.hpp#L63[boost/url/grammar/charset.hpp,window=blank_]>`

[source,cpp,subs="verbatim,macros,-callouts"]
----
template<class T>
using is_charset = pass:q[_see-below_];
----

=== Description


This metafunction determines if the
type `T` meets these requirements of
_CharSet_
:

* An instance of `T` is invocable
with this equivalent function signature:
[,cpp]
----
bool T::operator()( char ) const noexcept;
----

=== Use with `enable_if` on the return value:
[,cpp]
----
template< class CharSet >
typename std::enable_if< is_charset<T>::value >::type
func( CharSet const& cs );
----