]>
Commit | Line | Data |
---|---|---|
1 | [#first_of] | |
2 | [section first_of] | |
3 | ||
4 | [h1 Synopsis] | |
5 | ||
6 | template <class P1, /* ... */, class Pn> | |
7 | struct first_of; | |
8 | ||
9 | This is a [link parser_combinator parser combinator]. | |
10 | ||
11 | [table Arguments | |
12 | [[Name] [Type]] | |
13 | [[`P1` .. `Pn`] [[link parser parser]]] | |
14 | ] | |
15 | ||
16 | [h1 Description] | |
17 | ||
18 | `first_of` applies the `P1` ... `Pn` parsers in sequence. It accepts an input | |
19 | when all parsers accept it. The result of parsing is the result of the first | |
20 | parser. | |
21 | ||
22 | [h1 Header] | |
23 | ||
24 | #include <boost/metaparse/first_of.hpp> | |
25 | ||
26 | [h1 Expression semantics] | |
27 | ||
28 | For any `p1`, ... `pn` parsers | |
29 | ||
30 | first_of<p1, ..., pn> | |
31 | ||
32 | is equivalent to | |
33 | ||
34 | nth_of_c<0, p1, ..., pn> | |
35 | ||
36 | [h1 Example] | |
37 | ||
38 | #include <boost/metaparse/first_of.hpp> | |
39 | #include <boost/metaparse/int_.hpp> | |
40 | #include <boost/metaparse/lit_c.hpp> | |
41 | #include <boost/metaparse/string.hpp> | |
42 | #include <boost/metaparse/start.hpp> | |
43 | #include <boost/metaparse/is_error.hpp> | |
44 | #include <boost/metaparse/get_result.hpp> | |
45 | ||
46 | #include <type_traits> | |
47 | ||
48 | using namespace boost::metaparse; | |
49 | ||
50 | using int_with_semicolon = first_of<int_, lit_c<';'>>; | |
51 | ||
52 | static_assert( | |
53 | is_error< | |
54 | int_with_semicolon::apply<BOOST_METAPARSE_STRING("13"), start> | |
55 | >::type::value, | |
56 | "int without semicolon is rejected" | |
57 | ); | |
58 | ||
59 | static_assert( | |
60 | get_result< | |
61 | int_with_semicolon::apply<BOOST_METAPARSE_STRING("13;"), start> | |
62 | >::type::value, | |
63 | "the result is the result of the first parser" | |
64 | ); | |
65 | ||
66 | [endsect] | |
67 |