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_modifiers_index Index modifiers] | |
| 9 | ||
| 10 | Index modifiers can be used with the BOOST_VMD_ELEM macro | |
| 11 | when identifier modifiers are being used. Index modifiers | |
| 12 | take two values: | |
| 13 | ||
| 14 | * BOOST_VMD_RETURN_INDEX, return an index as a number, starting with 0, | |
| 15 | of the particular identifier modifier which matched, as part of the | |
| 16 | output of the BOOST_VMD_ELEM macro. If no particular identifier modifier | |
| 17 | matches, return emptiness as part of the output. The index number is | |
| 18 | determined purely by the order in which identifier modifiers are | |
| 19 | specified as optional parameters to BOOST_VMD_ELEM, whether singly as | |
| 20 | individual optional parameters or as a tuple of identifier modifiers. | |
| 21 | * BOOST_VMD_RETURN_NO_INDEX, do not return an index as part of the output. | |
| 22 | This is the default value and need only be used to override the | |
| 23 | BOOST_VMD_RETURN_INDEX value if it is specified. | |
| 24 | ||
| 25 | The BOOST_VMD_RETURN_INDEX tells the programmer which one of the identifier | |
| 26 | modifiers matched the element's data as an index. Some macro programmers | |
| 27 | find this more useful for the purposes of macro branching logic than | |
| 28 | branching using the actual name of the identifier itself. | |
| 29 | ||
| 30 | When the index modifier BOOST_VMD_RETURN_INDEX is specified, and identifier | |
| 31 | modifiers are specified along with the BOOST_VMD_TYPE_IDENTIFIER filter | |
| 32 | modifier, the output of BOOST_VMD_ELEM becomes a tuple of two elements. | |
| 33 | The first tuple element is the element matched and the last tuple element is the | |
| 34 | index, starting with 0, of the identifier modifier which matched. If an element | |
| 35 | is not matched both tuple elements are empty. | |
| 36 | ||
| 37 | If the splitting modifier BOOST_VMD_RETURN_AFTER is also specified then the | |
| 38 | output is a tuple of three elements. The first tuple element is the element matched, | |
| 39 | the second tuple element is the rest of the sequence after the matching element, | |
| 40 | and the last tuple element is the numeric index. If an element is not matched | |
| 41 | then all three tuple elements are empty. | |
| 42 | ||
| 43 | If identifier modifiers and the BOOST_VMD_TYPE_IDENTIFIER filter modifier | |
| 44 | are not specified as optional parameters, then if BOOST_VMD_RETURN_INDEX is | |
| 45 | specified it is ignored. If the splitting modifier BOOST_VMD_RETURN_ONLY_AFTER | |
| 46 | is specified, if BOOST_VMD_RETURN_INDEX is also specified it is ignored. | |
| 47 | ||
| 48 | Let's see how this works: | |
| 49 | ||
| 50 | #include <boost/vmd/elem.hpp> | |
| 51 | ||
| 52 | #define BOOST_VMD_REGISTER_ANAME (ANAME) | |
| 53 | #define BOOST_VMD_REGISTER_APLACE (APLACE) | |
| 54 | #define BOOST_VMD_REGISTER_ACOUNTRY (ACOUNTRY) | |
| 55 | ||
| 56 | #define BOOST_VMD_DETECT_ANAME_ANAME | |
| 57 | #define BOOST_VMD_DETECT_APLACE_APLACE | |
| 58 | ||
| 59 | #define A_SEQUENCE (1,2,3) ANAME (1)(2) 46 | |
| 60 | ||
| 61 | BOOST_VMD_ELEM(1,A_SEQUENCE,BOOST_VMD_TYPE_IDENTIFIER) will return 'ANAME' | |
| 62 | BOOST_VMD_ELEM(1,A_SEQUENCE,BOOST_VMD_TYPE_IDENTIFIER,APLACE,ACOUNTRY) will return emptiness | |
| 63 | BOOST_VMD_ELEM(1,A_SEQUENCE,BOOST_VMD_TYPE_IDENTIFIER,BOOST_VMD_RETURN_INDEX,APLACE,ACOUNTRY) will return (,) | |
| 64 | BOOST_VMD_ELEM(1,A_SEQUENCE,BOOST_VMD_TYPE_IDENTIFIER,BOOST_VMD_RETURN_INDEX,ANAME,APLACE,ACOUNTRY) will return '(ANAME,0)' | |
| 65 | BOOST_VMD_ELEM(1,A_SEQUENCE,BOOST_VMD_TYPE_IDENTIFIER,BOOST_VMD_RETURN_INDEX,(APLACE,ACOUNTRY,ANAME)) will return '(ANAME,2)' | |
| 66 | ||
| 67 | Used with splitting modifiers: | |
| 68 | ||
| 69 | #include <boost/vmd/elem.hpp> | |
| 70 | ||
| 71 | BOOST_VMD_ELEM(1,A_SEQUENCE,BOOST_VMD_TYPE_IDENTIFIER,BOOST_VMD_RETURN_INDEX,APLACE,ACOUNTRY,BOOST_VMD_RETURN_AFTER) will return (,,) | |
| 72 | BOOST_VMD_ELEM(1,A_SEQUENCE,BOOST_VMD_TYPE_IDENTIFIER,BOOST_VMD_RETURN_INDEX,ANAME,APLACE,ACOUNTRY,BOOST_VMD_RETURN_AFTER) will return '(ANAME,(1)(2) 46,0)' | |
| 73 | BOOST_VMD_ELEM(1,A_SEQUENCE,BOOST_VMD_TYPE_IDENTIFIER,BOOST_VMD_RETURN_INDEX,(APLACE,ACOUNTRY,ANAME),BOOST_VMD_RETURN_AFTER) will return '(ANAME,(1)(2) 46,2)' | |
| 74 | ||
| 75 | BOOST_VMD_ELEM(1,A_SEQUENCE,BOOST_VMD_TYPE_IDENTIFIER,BOOST_VMD_RETURN_INDEX,(APLACE,ACOUNTRY,ANAME),BOOST_VMD_RETURN_ONLY_AFTER) will return '(1)(2) 46' | |
| 76 | ||
| 77 | [endsect] |