2903. The form of initialization for the emplace-constructors is not specified

Section: 22.6.3.2 [variant.ctor] Status: C++17 Submitter: United States Opened: 2017-02-03 Last modified: 2020-09-06

Priority: Not Prioritized

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Discussion:

Addresses US 118

The form of initialization for the emplace-constructors is not specified. We are very clear to mandate "as if by direct non-list initialization" for each constructor in optional, so there is no ambiguity regarding parens vs. braces. That wording idiom should be followed by variant.

Proposed change: Insert the phrase "as if direct-non-list-initializing" at appropriate locations in paragraphs 19, 23, 27, and 31

[2017-02-20, Marshall adds wording]

[2017-02-27, Marshall adds wording to cover two more cases]

Previous resolution [SUPERSEDED]:

This wording is relative to N4640.

  1. Modify 22.6.3.2 [variant.ctor] paragraph 19 as indicated:

    Effects: Initializes the contained value as if direct-non-list-initializing an object of type T with the arguments std::forward<Args>(args)....

  2. Modify 22.6.3.2 [variant.ctor] paragraph 23 as indicated:

    Effects: Initializes the contained value as if direct-non-list-initializingconstructing an object of type T with the arguments il, std::forward<Args>(args)....

  3. Modify 22.6.3.2 [variant.ctor] paragraph 27 as indicated:

    Effects: Initializes the contained value as if direct-non-list-initializingconstructing an object of type TI with the arguments std::forward<Args>(args)....

  4. Modify 22.6.3.2 [variant.ctor] paragraph 31 as indicated:

    Effects: Initializes the contained value as if direct-non-list-initializingconstructing an object of type TI with the arguments il, std::forward(args)....

[Kona 2017-02-28]

Accepted as Immediate to resolve NB comment.

Proposed resolution:

This wording is relative to N4640.

  1. Modify 22.6.3.2 [variant.ctor] paragraph 19 as indicated:

    Effects: Initializes the contained value as if direct-non-list-initializing an object of type T with the arguments std::forward<Args>(args)....

  2. Modify 22.6.3.2 [variant.ctor] paragraph 23 as indicated:

    Effects: Initializes the contained value as if direct-non-list-initializingconstructing an object of type T with the arguments il, std::forward<Args>(args)....

  3. Modify 22.6.3.2 [variant.ctor] paragraph 27 as indicated:

    Effects: Initializes the contained value as if direct-non-list-initializingconstructing an object of type TI with the arguments std::forward<Args>(args)....

  4. Modify 22.6.3.2 [variant.ctor] paragraph 31 as indicated:

    Effects: Initializes the contained value as if direct-non-list-initializingconstructing an object of type TI with the arguments il, std::forward(args)....

  5. Modify 22.6.3.5 [variant.mod] paragraph 6 as indicated:

    Effects: Destroys the currently contained value if valueless_by_exception() is false. Then direct-initializes the contained value as if direct-non-list-initializingconstructing a value of type TI with the arguments std::forward<Args>(args)....

  6. Modify 22.6.3.5 [variant.mod] paragraph 11 as indicated:

    Effects: Destroys the currently contained value if valueless_by_exception() is false. Then direct-initializes the contained value as if direct-non-list-initializingconstructing a value of type TI with the arguments il, std::forward<Args>(args)....