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Section: 220.127.116.11 [allocator.requirements] Status: C++20 Submitter: United States Opened: 2019-11-04 Last modified: 2021-02-25
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Addresses US 162/US 163
US 162:The default behavior for a.destroy is now to call destroy_at Proposed change: Replace "default" entry with: destroy_at(c)
US 163:The default behavior for a.construct is now to call construct_at Proposed change: Replace "default" entry with: construct_at(c, std::forward<Args>(args)...) Dietmar Kühl: In Table 34 [tab:cpp17.allocator] the behavior of a.construct(c, args) and a.destroy(c) are described to have a default behavior of ::new ((void*)c) C(forward<Args>(args)) and c->~C(), respectively. However, this table doesn't actually define what is happening if these operations are omitted: The behavior is provided when using an allocator is used via std::allocator_traits and is, thus, defined by the corresponding std::allocator_traits functions. These functions are specified in 18.104.22.168 [allocator.traits.members] paragraphs 5 and 6 to call construct_at(c, std::forward<Args>(args) and destroy_at(p), respectively. The text in the table should be updated to match the actual behavior.
[2019-11 Status to Ready during Wednesday morning issue processing in Belfast.]
This wording is relative to N4835.
Modify 22.214.171.124 [allocator.requirements], Table [tab:cpp17.allocator] "Cpp17Allocator requirements" as indicated:
Table 34 — Cpp17Allocator requirements [tab:cpp17.allocator] Expression Return type Assertion/note
Default … a.construct(c, args) (not used) Effects: Constructs an object of type C at c ::new ((void*)c) C(forward<Args>(args)...) a.destroy(c) (not used) Effects: Destroys the object at c c->~C() …