Issue 2081: Allocator requirements should include CopyConstructible (original) (raw)

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2081. Allocator requirements should include CopyConstructible

Section: 16.4.4.6 [allocator.requirements] Status: C++14 Submitter: Jonathan Wakely Opened: 2011-08-30 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

As discussed in c++std-lib-31054 and c++std-lib-31059, the Allocatorrequirements implicitly require CopyConstructible becausea.select_on_container_copy_construction() andcontainer.get_allocator() both return a copy by value, but the requirement is not stated explicitly anywhere.

In order to clarify that allocators cannot have 'explicit' copy constructors, the requirements should include CopyConstructible.

[2012, Kona]

Move to Ready.

[2012, Portland: applied to WP]

Proposed resolution:

This wording is relative to the FDIS.

1. Change Table 28 — Allocator requirements in 16.4.4.6 [allocator.requirements]:
   Table 28 — Allocator requirements

   Expression	Return type	Assertion/note pre-/post-condition	Default
   X a1(a); X a1 = a;		Shall not exit via an exception.post: a1 == a
   …

| X a1(move(a)); X a1 = move(a); | | Shall not exit via an exception.post: a1 equals the prior valueof a. | | 2. Change 16.4.4.6 [allocator.requirements] paragraph 4:

An allocator type X shall satisfy the requirements of CopyConstructible(16.4.4.2 [utility.arg.requirements]). The X::pointer, X::const_pointer, X::void_pointer, and X::const_void_pointer types shall satisfy the requirements of NullablePointer (16.4.4.4 [nullablepointer.requirements]). No constructor, comparison operator, copy operation, move operation, or swap operation on these types shall exit via an exception. X::pointer and X::const_pointer shall also satisfy the requirements for a random access iterator (24.3 [iterator.requirements]).