CWG2895 [dcl.init.general] should ignore cv-qualification of destination type

[t3nsor]

Full name of submitter: Brian Bi

Reference (section label): [dcl.init.general]

Issue description: CWG2830 clarified that list-initialization of cv T follows the same rules as list-initialization of T. We need to do something similar for non-list-initialization:

• p16.3 needs to also apply to arrays of the cv-qualified versions of char8_t, char16_t, etc.
• p16.8 needs to also apply to cv bool.

Suggested resolution:

Drafting note: This suggested resolution follows the approach in CWG2830, where we strip the cv-qualifiers at the very beginning. This will avoid the need to address the issue again when P3087R0 comes up for Core review.

Edit the preamble of [dcl.init.general]/16:

The semantics of initializers are as follows. The destination type is the cv-unqualified type of the object or reference being initialized and the source type is the type of the initializer expression. If the initializer is not a single (possibly parenthesized) expression, the source type is not defined.

Edit the preamble of [dcl.init.general]/16.6:

Otherwise, if the destination type is a ~(possibly cv-qualified)~ class type:

Edit [dcl.init.general]/16.6.1:

If the initializer expression is a prvalue and the cv-unqualified version of the source type is the same ~class as the class of the destination~ as the destination type, the initializer expression is used to initialize the destination object.

Edit the preamble of [dcl.init.general]/16.6.2:

Otherwise, if the initialization is direct-initialization, or if it is copy-initialization where the cv-unqualified version of the source type is the same ~class as, or a derived class of, the class of the destination~ as or is derived from the destination type, constructors are considered. The applicable constructors are enumerated ([over.match.ctor]), and the best one is chosen through overload resolution ([over.match]). Then:

Edit [dcl.init.general]/16.9:

Otherwise, the initial value of the object being initialized is the (possibly converted) value of the initializer expression. A standard conversion sequence ([conv]) is used to convert the initializer expression to a prvalue of the ~cv-unqualified version of the~ destination type; no user-defined conversions are considered. If the conversion cannot be done, the initialization is ill-formed. When initializing a bit-field with a value that it cannot represent, the resulting value of the bit-field is implementation-defined.

[jensmaurer]

CWG2895