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2307. Should the Standard Library use explicit only when necessary?

Section: 23 [containers] Status: LEWG Submitter: Zhihao Yuan Opened: 2013-09-26 Last modified: 2018-11-12

Priority: 2

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Discussion:

LWG 2193(i) yields explicit for default ctors to allow {}, but not for all cases of uniform initialization. For example: 

explicit vector(size_type count, const Allocator& alloc = Allocator());

This prevents {n, alloc()}. Although this use is relatively rare, but the behavior is inconsistent with that of 

vector(size_type count, const T& value, const Allocator& alloc = Allocator());

[Urbana 2014-11-07: Move to Open]

[2018-08 Batavia Monday issue discussion]

This really needs a paper; splitting a lot of constructors. Nevin to write paper.

[2018-11 San Diego Thursday night issue processing]

LEWG has rejected Nevin's paper, so they need to formulate a policy.

Proposed resolution: