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- [#is_digit]
- [section is_digit]
- [h1 Synopsis]
- namespace util
- {
- template <class C>
- struct is_digit;
- }
- This is a [link lazy_metafunction lazy template metafunction] that supports
- [link currying currying].
- [table Arguments
- [[Name] [Type]]
- [[`C`] [[link boxed_value boxed] character value]]
- ]
- [h1 Description]
- Checks if `C` is a digit value or not. Returns a boxed boolean value.
- [h1 Header]
- #include <boost/metaparse/util/is_digit.hpp>
- [h1 Expression semantics]
- The following expressions are equivalent:
- is_digit<boost::mpl::char_<'0'>>::type
- is_digit<>::apply<boost::mpl::char_<'0'>>::type
- boost::mpl::true_
- The following expressions are also equivalent:
- is_digit<>::apply<c>::type
- boost::mpl::false_
- [h1 Example]
- #include <boost/metaparse/util/is_digit.hpp>
-
- #include <type_traits>
-
- using namespace boost::metaparse;
-
- struct returns_char
- {
- using type = std::integral_constant<char, '0'>;
- };
-
- static_assert(
- util::is_digit<std::integral_constant<char, '0'>>::type::value,
- "digit character should be a digit"
- );
-
- static_assert(
- !util::is_digit<std::integral_constant<char, 'x'>>::type::value,
- "letter should not be a digit"
- );
-
- static_assert(
- util::is_digit<>::type::apply<std::integral_constant<char, '0'>>::type::value,
- "it should support currying"
- );
-
- static_assert(
- util::is_digit<returns_char>::type::value,
- "it should support lazy evaluation"
- );
- [endsect]
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