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7c673cae FG |
1 | [#digit_val] |
2 | [section digit_val] | |
3 | ||
4 | [h1 Synopsis] | |
5 | ||
6 | struct digit_val; | |
7 | ||
8 | This is a [link parser parser]. | |
9 | ||
10 | [h1 Description] | |
11 | ||
12 | It accepts one character in the range `0-9`. The result of the parser is the | |
13 | value represented by the accepted character. | |
14 | ||
15 | [h1 Header] | |
16 | ||
17 | #include <boost/metaparse/digit_val.hpp> | |
18 | ||
19 | [h1 Expression semantics] | |
20 | ||
21 | The following are equivalent: | |
22 | ||
23 | digit_val | |
24 | ||
25 | transform<digit, util::digit_to_int<>> | |
26 | ||
27 | [h1 Example] | |
28 | ||
29 | #include <boost/metaparse/digit_val.hpp> | |
30 | #include <boost/metaparse/start.hpp> | |
31 | #include <boost/metaparse/string.hpp> | |
32 | #include <boost/metaparse/is_error.hpp> | |
33 | #include <boost/metaparse/get_result.hpp> | |
34 | ||
35 | using namespace boost::metaparse; | |
36 | ||
37 | static_assert( | |
38 | !is_error<digit_val::apply<BOOST_METAPARSE_STRING("0"), start>>::type::value, | |
39 | "digit_val should accept a digit" | |
40 | ); | |
41 | ||
42 | static_assert( | |
43 | is_error<digit_val::apply<BOOST_METAPARSE_STRING("x"), start>>::type::value, | |
44 | "digit_val should reject a character" | |
45 | ); | |
46 | ||
47 | static_assert( | |
48 | get_result< | |
49 | digit_val::apply<BOOST_METAPARSE_STRING("0"), start> | |
50 | >::type::value == 0, | |
51 | "the result of parsing should be the int value" | |
52 | ); | |
53 | ||
54 | [endsect] | |
55 |