[#boost-urls-grammar-is_rule]
= xref:boost.adoc[boost]::xref:boost/urls.adoc[urls]::xref:boost/urls/grammar.adoc[grammar]::is_rule
:relfileprefix: ../../../
:mrdocs:


Determine if T meets the requirements of xref:boost/urls/grammar/Rule.adoc[Rule]

== Synopsis


Declared in `<https://www.github.com/boostorg/url/blob/develop/include/boost/url/grammar/type_traits.hpp#L62[boost/url/grammar/type_traits.hpp]>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class T>
using is_rule = /* implementation-defined */::xref:boost/urls/grammar/implementation_defined/is_rule.adoc[is_rule]<T>;
----

== Description


This is an alias for `std::true_type` if    `T` meets the requirements, otherwise it    is an alias for `std::false_type`.


=== Example

[,cpp]
----
struct U
{
    struct value_type;

    auto
    parse(
        char const*& it,
        char const* end) const ->
            system::result<value_type>
};

static_assert( is_rule<U>::value, "Requirements not met" );
----


== See Also


xref:boost/urls/grammar/parse-02.adoc[parse]&period;






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