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7c673cae FG |
1 | [#is_whitespace] |
2 | [section is_whitespace] | |
3 | ||
4 | [h1 Synopsis] | |
5 | ||
6 | namespace util | |
7 | { | |
8 | template <class C> | |
9 | struct is_whitespace; | |
10 | } | |
11 | ||
12 | This is a [link lazy_metafunction lazy template metafunction] that supports | |
13 | [link currying currying]. | |
14 | ||
15 | [table Arguments | |
16 | [[Name] [Type]] | |
17 | [[`C`] [[link boxed_value boxed] character value]] | |
18 | ] | |
19 | ||
20 | [h1 Description] | |
21 | ||
22 | Checks if `C` is a whitespace character. Returns a boxed boolean value. | |
23 | ||
24 | [h1 Header] | |
25 | ||
26 | #include <boost/metaparse/util/is_whitespace.hpp> | |
27 | ||
28 | [h1 Expression semantics] | |
29 | ||
30 | For any `C` nullary template metafunction returning a wrapped character value | |
31 | the following are equivalent: | |
32 | ||
33 | is_whitespace<C>::type | |
34 | is_whitespace<>::type::apply<C>::type | |
35 | is_whitespace_c<C::type::value>::type | |
36 | ||
37 | [h1 Example] | |
38 | ||
39 | #include <boost/metaparse/util/is_whitespace.hpp> | |
40 | ||
41 | #include <type_traits> | |
42 | ||
43 | using namespace boost::metaparse; | |
44 | ||
45 | struct returns_char | |
46 | { | |
47 | using type = std::integral_constant<char, ' '>; | |
48 | }; | |
49 | ||
50 | static_assert( | |
51 | util::is_whitespace<std::integral_constant<char, ' '>>::type::value, | |
52 | "a space should be a whitespace character" | |
53 | ); | |
54 | ||
55 | static_assert( | |
56 | !util::is_whitespace<std::integral_constant<char, '0'>>::type::value, | |
57 | "a number should not be a whitespace character" | |
58 | ); | |
59 | ||
60 | static_assert( | |
61 | util::is_whitespace<>::type | |
62 | ::apply<std::integral_constant<char, '\t'>>::type::value, | |
63 | "it should support currying" | |
64 | ); | |
65 | ||
66 | static_assert( | |
67 | util::is_whitespace<returns_char>::type::value, | |
68 | "it should support lazy evaluation" | |
69 | ); | |
70 | ||
71 | [endsect] | |
72 |