From Jason Turner

[allocator.uses]

C++14 → C++17 3.5 KB 41 lines
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tmp/tmppwnphjjm/{from.md → to.md} RENAMED
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  ``` cpp
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  template <class T, class Alloc> struct uses_allocator;
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  ```
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- automatically detects whether `T` has a nested `allocator_type` that is
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- convertible from `Alloc`. Meets the BinaryTypeTrait
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- requirements ([[meta.rqmts]]). The implementation shall provide a
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- definition that is derived from `true_type` if a type
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- `T::allocator_type` exists and
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- `is_convertible<Alloc, T::allocator_type>::value != false`, otherwise it
 
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  shall be derived from `false_type`. A program may specialize this
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  template to derive from `true_type` for a user-defined type `T` that
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  does not have a nested `allocator_type` but nonetheless can be
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  constructed with an allocator where either:
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  - the first argument of a constructor has type `allocator_arg_t` and the
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  second argument has type `Alloc` or
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  - the last argument of a constructor has type `Alloc`.
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- #### uses-allocator construction <a id="allocator.uses.construction">[[allocator.uses.construction]]</a>
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  *Uses-allocator construction* with allocator `Alloc` refers to the
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  construction of an object `obj` of type `T`, using constructor arguments
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  `v1, v2, ..., vN` of types `V1, V2, ..., VN`, respectively, and an
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  allocator `alloc` of type `Alloc`, according to the following rules:
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- - if `uses_allocator<T, Alloc>::value` is `false` and
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- `is_constructible<T, V1, V2, ..., VN>::value` is `true`, then `obj` is
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  initialized as `obj(v1, v2, ..., vN)`;
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- - otherwise, if `uses_allocator<T, Alloc>::value` is `true` and
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- `is_constructible<T, allocator_arg_t, Alloc,`
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- `V1, V2, ..., VN>::value` is `true`, then `obj` is initialized as
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- `obj(allocator_arg, alloc, v1,
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  v2, ..., vN)`;
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- - otherwise, if `uses_allocator<T, Alloc>::value` is `true` and
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- `is_constructible<T, V1, V2, ..., VN, Alloc>::value` is `true`, then
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- `obj` is initialized as `obj(v1, v2, ..., vN, alloc)`;
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  - otherwise, the request for uses-allocator construction is ill-formed.
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- An error will result if `uses_allocator<T, Alloc>::value` is `true`
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- but the specific constructor does not take an allocator. This
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  definition prevents a silent failure to pass the allocator to an
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- element.
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  ``` cpp
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  template <class T, class Alloc> struct uses_allocator;
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  ```
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+ *Remarks:* Automatically detects whether `T` has a nested
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+ `allocator_type` that is convertible from `Alloc`. Meets the
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+ `BinaryTypeTrait` requirements ([[meta.rqmts]]). The implementation
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+ shall provide a definition that is derived from `true_type` if the
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+ *qualified-id* `T::allocator_type` is valid and denotes a
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+ type ([[temp.deduct]]) and
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+ `is_convertible_v<Alloc, T::allocator_type> != false`, otherwise it
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  shall be derived from `false_type`. A program may specialize this
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  template to derive from `true_type` for a user-defined type `T` that
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  does not have a nested `allocator_type` but nonetheless can be
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  constructed with an allocator where either:
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  - the first argument of a constructor has type `allocator_arg_t` and the
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  second argument has type `Alloc` or
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  - the last argument of a constructor has type `Alloc`.
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+ #### Uses-allocator construction <a id="allocator.uses.construction">[[allocator.uses.construction]]</a>
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  *Uses-allocator construction* with allocator `Alloc` refers to the
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  construction of an object `obj` of type `T`, using constructor arguments
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  `v1, v2, ..., vN` of types `V1, V2, ..., VN`, respectively, and an
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  allocator `alloc` of type `Alloc`, according to the following rules:
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+ - if `uses_allocator_v<T, Alloc>` is `false` and
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+ `is_constructible_v<T, V1, V2, ..., VN>` is `true`, then `obj` is
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  initialized as `obj(v1, v2, ..., vN)`;
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+ - otherwise, if `uses_allocator_v<T, Alloc>` is `true` and
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+ `is_constructible_v<T, allocator_arg_t, Alloc,` `V1, V2, ..., VN>` is
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+ `true`, then `obj` is initialized as `obj(allocator_arg, alloc, v1,
 
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  v2, ..., vN)`;
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+ - otherwise, if `uses_allocator_v<T, Alloc>` is `true` and
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+ `is_constructible_v<T, V1, V2, ..., VN, Alloc>` is `true`, then `obj`
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+ is initialized as `obj(v1, v2, ..., vN, alloc)`;
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  - otherwise, the request for uses-allocator construction is ill-formed.
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+ \[*Note 1*: An error will result if `uses_allocator_v<T, Alloc>` is
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+ `true` but the specific constructor does not take an allocator. This
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  definition prevents a silent failure to pass the allocator to an
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+ element. — *end note*]
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