projects / ceph.git / blame
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|---|---|---|
| 7c673cae FG |
1 | .. Metafunctions/Concepts//Trivial Metafunction |70 |
| 2 | ||
| 3 | Trivial Metafunction | |
| 4 | ==================== | |
| 5 | ||
| 6 | Description | |
| 7 | ----------- | |
| 8 | ||
| 9 | A |Trivial Metafunction| accepts a single argument of a class type ``x`` and | |
| 10 | returns the ``x``\ 's nested type member ``x::name``, where ``name`` is | |
| 11 | a placeholder token for the actual member's name accessed by a specific | |
| 12 | metafunction's instance. By convention, all `trivial metafunctions`__ in MPL | |
| 13 | are named after the members they provide assess to. For instance, a |Trivial | |
| 14 | Metafunction| named ``first`` reaches for the ``x``\ 's nested member | |
| 15 | ``::first``. | |
| 16 | ||
| 17 | __ `Trivial Metafunctions Summary`_ | |
| 18 | ||
| 19 | ||
| 20 | Expression requirements | |
| 21 | ----------------------- | |
| 22 | ||
| 23 | |In the following table...| ``name`` is placeholder token for the names of | |
| 24 | the |Trivial Metafunction| itself and the accessed member, and ``x`` is | |
| 25 | a class type such that ``x::name`` is a valid *type-name*. | |
| 26 | ||
| 27 | +---------------------------+-------------------+---------------------------+ | |
| 28 | | Expression | Type | Complexity | | |
| 29 | +===========================+===================+===========================+ | |
| 30 | | ``name<x>::type`` | Any type | Constant time. | | |
| 31 | +---------------------------+-------------------+---------------------------+ | |
| 32 | ||
| 33 | ||
| 34 | Expression semantics | |
| 35 | -------------------- | |
| 36 | ||
| 37 | .. parsed-literal:: | |
| 38 | ||
| 39 | typedef name<x>::type r; | |
| 40 | ||
| 41 | :Precondition: | |
| 42 | ``x::name`` is a valid *type-name*. | |
| 43 | ||
| 44 | :Semantics: | |
| 45 | ``is_same<r,x::name>::value == true``. | |
| 46 | ||
| 47 | ||
| 48 | Models | |
| 49 | ------ | |
| 50 | ||
| 51 | * |first| | |
| 52 | * |second| | |
| 53 | * |base| | |
| 54 | ||
| 55 | ||
| 56 | See also | |
| 57 | -------- | |
| 58 | ||
| 59 | |Metafunctions|, |Trivial Metafunctions|, |identity| | |
| 60 | ||
| 61 | ||
| 62 |