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