projects / ceph.git / blame
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| 2 | (C) Copyright Edward Diener 2011-2015 | |
| 3 | Distributed under the Boost Software License, Version 1.0. | |
| 4 | (See accompanying file LICENSE_1_0.txt or copy at | |
| 5 | http://www.boost.org/LICENSE_1_0.txt). | |
| 6 | ] | |
| 7 | ||
| 8 | [section:vmd_type Types] | |
| 9 | ||
| 10 | A subset of identifiers is VMD types, called a 'v-type'. These are identifiers | |
| 11 | which represent all of the preprocessor data types which VMD can parse. This subset of | |
| 12 | identifiers is automatically registered and pre-detected by VMD. Each identifier | |
| 13 | type begins with the unique prefix 'BOOST_VMD_TYPE_'. | |
| 14 | ||
| 15 | The actual types are: | |
| 16 | ||
| 17 | * BOOST_VMD_TYPE_EMPTY, represents emptiness, ie. "empty data" | |
| 18 | * BOOST_VMD_TYPE_ARRAY, a Boost PP array | |
| 19 | * BOOST_VMD_TYPE_LIST, a Boost PP list | |
| 20 | * BOOST_VMD_TYPE_SEQ, a Boost PP seq | |
| 21 | * BOOST_VMD_TYPE_TUPLE, a Boost PP tuple | |
| 22 | * BOOST_VMD_TYPE_IDENTIFIER, identifier | |
| 23 | * BOOST_BMD_TYPE_NUMBER, a number | |
| 24 | * BOOST_VMD_TYPE_TYPE, a type itself | |
| 25 | * BOOST_VMD_TYPE_SEQUENCE, a sequence | |
| 26 | * BOOST_VMD_TYPE_UNKNOWN, an unknown type | |
| 27 | ||
| 28 | Since a v-type is itself an identifier the particular constraint on the input | |
| 29 | to test is exactly the same as for identifiers. | |
| 30 | ||
| 31 | The constraint is that the beginning input character, ignoring any whitespace, passed | |
| 32 | as the input to test must be either: | |
| 33 | ||
| 34 | * an identifier character, ie. an alphanumeric or an underscore | |
| 35 | * the left parenthesis of a tuple | |
| 36 | ||
| 37 | and if the first character is not the left parenthesis of a tuple | |
| 38 | the remaining characters must be alphanumeric or an underscore until a space character | |
| 39 | or end of input occurs. | |
| 40 | ||
| 41 | If this is not the case the behavior is undefined, and most likely | |
| 42 | a preprocessing error will occur. | |
| 43 | ||
| 44 | The macro used to test for a particular type in VMD is called BOOST_VMD_IS_TYPE. | |
| 45 | The macro takes a single parameter, the input to test against. | |
| 46 | ||
| 47 | The macro returns 1 if the parameter is a v-type, otherwise the macro returns 0. | |
| 48 | ||
| 49 | A v-type is also an identifier, which has been registered and pre-detected, | |
| 50 | so you can also use the VMD functionality which works with identifiers to work with | |
| 51 | a v-type as an identifier if you like. | |
| 52 | ||
| 53 | [heading Example] | |
| 54 | ||
| 55 | Let us look at an example of how to use BOOST_VMD_IS_TYPE. | |
| 56 | ||
| 57 | #include <boost/vmd/is_type.hpp> | |
| 58 | ||
| 59 | BOOST_VMD_IS_TYPE(input) | |
| 60 | ||
| 61 | returns: | |
| 62 | ||
| 63 | if input = BOOST_VMD_TYPE_SEQ, 1 | |
| 64 | if input = BOOST_VMD_TYPE_NUMBER, 1 | |
| 65 | if input = SQUARE, 0 | |
| 66 | if input = BOOST_VMD_TYPE_IDENTIFIER DATA, 0 since there are tokens after the type | |
| 67 | if input = %44, does not meet the constraint therefore undefined behavior | |
| 68 | if input = ( BOOST_VMD_TYPE_EMPTY ), 0 since the macro begins with a tuple and this can be tested for | |
| 69 | ||
| 70 | [heading Usage] | |
| 71 | ||
| 72 | To use the BOOST_VMD_IS_TYPE macro either include the general header: | |
| 73 | ||
| 74 | #include <boost/vmd/vmd.hpp> | |
| 75 | ||
| 76 | or include the specific header: | |
| 77 | ||
| 78 | #include <boost/vmd/is_type.hpp> | |
| 79 | ||
| 80 | [endsect] |