projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | .. Metafunctions/Composition and Argument Binding//protect |60 |
| 2 | ||
| 3 | protect | |
| 4 | ======= | |
| 5 | ||
| 6 | Synopsis | |
| 7 | -------- | |
| 8 | ||
| 9 | .. parsed-literal:: | |
| 10 | ||
| 11 | template< | |
| 12 | typename F | |
| 13 | > | |
| 14 | struct protect | |
| 15 | { | |
| 16 | // |unspecified| | |
| 17 | // |...| | |
| 18 | }; | |
| 19 | ||
| 20 | ||
| 21 | ||
| 22 | Description | |
| 23 | ----------- | |
| 24 | ||
| 25 | ``protect`` is an identity wrapper for a |Metafunction Class| that prevents | |
| 26 | its argument from being recognized as a |bind expression|. | |
| 27 | ||
| 28 | ||
| 29 | Header | |
| 30 | ------ | |
| 31 | ||
| 32 | .. parsed-literal:: | |
| 33 | ||
| 34 | #include <boost/mpl/protect.hpp> | |
| 35 | ||
| 36 | ||
| 37 | Parameters | |
| 38 | ---------- | |
| 39 | ||
| 40 | +---------------+---------------------------+---------------------------------------+ | |
| 41 | | Parameter | Requirement | Description | | |
| 42 | +===============+===========================+=======================================+ | |
| 43 | | ``F`` | |Metafunction Class| | A metafunction class to wrap. | | |
| 44 | +---------------+---------------------------+---------------------------------------+ | |
| 45 | ||
| 46 | ||
| 47 | Expression semantics | |
| 48 | -------------------- | |
| 49 | ||
| 50 | For any |Metafunction Class| ``f``: | |
| 51 | ||
| 52 | ||
| 53 | .. parsed-literal:: | |
| 54 | ||
| 55 | typedef protect<f> g; | |
| 56 | ||
| 57 | :Return type: | |
| 58 | |Metafunction Class|. | |
| 59 | ||
| 60 | :Semantics: | |
| 61 | If ``f`` is a |bind expression|, equivalent to | |
| 62 | ||
| 63 | .. parsed-literal:: | |
| 64 | ||
| 65 | struct g | |
| 66 | { | |
| 67 | template< | |
| 68 | typename U1 = |unspecified|\,\ |...| typename U\ *n* = |unspecified| | |
| 69 | > | |
| 70 | struct apply | |
| 71 | : apply_wrap\ *n*\<f,U1,\ |...|\ U\ *n*\ > | |
| 72 | { | |
| 73 | }; | |
| 74 | }; | |
| 75 | ||
| 76 | otherwise equivalent to ``typedef f g;``. | |
| 77 | ||
| 78 | ||
| 79 | Example | |
| 80 | ------- | |
| 81 | ||
| 82 | .. parsed-literal:: | |
| 83 | ||
| 84 | struct f | |
| 85 | { | |
| 86 | template< typename T1, typename T2 > struct apply | |
| 87 | { | |
| 88 | typedef T2 type; | |
| 89 | }; | |
| 90 | }; | |
| 91 | ||
| 92 | typedef bind< quote\ ``3``\<if\_>,_1,_2,bind<f,_1,_2> > b1; | |
| 93 | typedef bind< quote\ ``3``\<if\_>,_1,_2,protect< bind<f,_1,_2> > > b2; | |
| 94 | ||
| 95 | typedef apply_wrap\ ``2``\< b1,false\_,char >::type r1; | |
| 96 | typedef apply_wrap\ ``2``\< b2,false\_,char >::type r2; | |
| 97 | ||
| 98 | BOOST_MPL_ASSERT(( is_same<r1,char> )); | |
| 99 | BOOST_MPL_ASSERT(( is_same<r2,protect< bind<f,_1,_2> > > )); | |
| 100 | ||
| 101 | ||
| 102 | See also | |
| 103 | -------- | |
| 104 | ||
| 105 | |Composition and Argument Binding|, |Invocation|, |bind|, |quote|, |apply_wrap| | |
| 106 | ||
| 107 | ||
| 108 |