projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | .. Metafunctions/Concepts//Metafunction |10 |
| 2 | ||
| 3 | Metafunction | |
| 4 | ============ | |
| 5 | ||
| 6 | Description | |
| 7 | ----------- | |
| 8 | ||
| 9 | .. _`nullary-metafunction`: | |
| 10 | ||
| 11 | A *metafunction* is a class or a class template that represents a | |
| 12 | function invocable at compile-time. An non-nullary metafunction is | |
| 13 | invoked by instantiating the class template with particular | |
| 14 | template parameters (metafunction arguments); the result of the | |
| 15 | metafunction application is accessible through the instantiation's | |
| 16 | nested ``type`` typedef. All metafunction's arguments must be types | |
| 17 | (i.e. only *type template parameters* are allowed). A metafunction | |
| 18 | can have a variable number of parameters. A *nullary metafunction* is | |
| 19 | represented as a (template) class with a nested ``type`` typename | |
| 20 | member. | |
| 21 | ||
| 22 | .. |nullary metafunction| replace:: `nullary-metafunction`_ | |
| 23 | ||
| 24 | ||
| 25 | Expression requirements | |
| 26 | ----------------------- | |
| 27 | ||
| 28 | |In the following table...| ``f`` is a |Metafunction|. | |
| 29 | ||
| 30 | +-------------------------------+-----------------------+---------------------------+ | |
| 31 | | Expression | Type | Complexity | | |
| 32 | +===============================+=======================+===========================+ | |
| 33 | | ``f::type`` | Any type | Unspecified. | | |
| 34 | +-------------------------------+-----------------------+---------------------------+ | |
| 35 | | ``f<>::type`` | Any type | Unspecified. | | |
| 36 | +-------------------------------+-----------------------+---------------------------+ | |
| 37 | | ``f<a1,..,an>::type`` | Any type | Unspecified. | | |
| 38 | +-------------------------------+-----------------------+---------------------------+ | |
| 39 | ||
| 40 | ||
| 41 | Expression semantics | |
| 42 | -------------------- | |
| 43 | ||
| 44 | .. parsed-literal:: | |
| 45 | ||
| 46 | typedef f::type x; | |
| 47 | ||
| 48 | :Precondition: | |
| 49 | ``f`` is a nullary |Metafunction|; ``f::type`` is a *type-name*. | |
| 50 | ||
| 51 | :Semantics: | |
| 52 | ``x`` is the result of the metafunction invocation. | |
| 53 | ||
| 54 | ||
| 55 | .. ................................................................................... | |
| 56 | ||
| 57 | .. parsed-literal:: | |
| 58 | ||
| 59 | typedef f<>::type x; | |
| 60 | ||
| 61 | :Precondition: | |
| 62 | ``f`` is a nullary |Metafunction|; ``f<>::type`` is a *type-name*. | |
| 63 | ||
| 64 | :Semantics: | |
| 65 | ``x`` is the result of the metafunction invocation. | |
| 66 | ||
| 67 | ||
| 68 | .. ................................................................................... | |
| 69 | ||
| 70 | .. parsed-literal:: | |
| 71 | ||
| 72 | typedef f<a1,\ |...| \a\ *n*\>::type x; | |
| 73 | ||
| 74 | :Precondition: | |
| 75 | ``f`` is an *n*-ary |Metafunction|; |a1...an| are types; | |
| 76 | ``f<a1,...an>::type`` is a *type-name*. | |
| 77 | ||
| 78 | :Semantics: | |
| 79 | ``x`` is the result of the metafunction invocation | |
| 80 | with the actual arguments |a1...an|. | |
| 81 | ||
| 82 | ||
| 83 | Models | |
| 84 | ------ | |
| 85 | ||
| 86 | * |identity| | |
| 87 | * |plus| | |
| 88 | * |begin| | |
| 89 | * |insert| | |
| 90 | * |fold| | |
| 91 | ||
| 92 | ||
| 93 | See also | |
| 94 | -------- | |
| 95 | ||
| 96 | |Metafunctions|, |Metafunction Class|, |Lambda Expression|, |Invocation|, |apply|, |lambda|, |bind| | |
| 97 | ||
| 98 | ||
| 99 |