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[dcl.type.auto.deduct]/2.3 superfluous? #2938

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tjs137 opened this issue Jun 21, 2019 · 1 comment
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[dcl.type.auto.deduct]/2.3 superfluous? #2938

tjs137 opened this issue Jun 21, 2019 · 1 comment
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@tjs137
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tjs137 commented Jun 21, 2019

[dcl.type.auto.deduct]/2(.3) directly provides placeholder type deduction for a non-type template parameter.

A type T containing a placeholder type, and a corresponding initializer e, are determined as follows:

  • …
  • for a non-type template parameter declared with a type that contains a placeholder type, T is the declared type of the non-type template parameter and e is the corresponding template argument.

[temp.arg.nontype]/1 provides the same thing

If the type T of a template-parameter contains a placeholder type or a placeholder for a deduced class type, the type of the parameter is the type deduced for the variable x in the invented declaration T x =template-argument;

but by using [dcl.type.auto.deduct]/2.2

  • for a variable declared with a type that contains a placeholder type, T is the declared type of the variable and e is the initializer. …

With that, it doesn't seem like [dcl.type.auto.deduct]/2.3 is necessary. Besides, [dcl.type.class.deduct] does not directly provide for replacement of deduced class type placeholders in non-type template parameters, only in an initializing variable declaration.
@jensmaurer jensmaurer added the decision-required A decision of the editorial group (or the Project Editor) is required. label Jun 24, 2019
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Editorial meeting: Prefer defining an abstract operations and using it when defining concrete operations, instead of defining a concrete operation and defining other concrete operations on top of that. temp.arg.nontype approach is less pleasing; remove that and keep dcl.type.auto.deduct. In temp.arg.non.type, say "the type of the parameter is deduced as specified in dcl.type.auto.deduct".
9.1.7.6 does not cover non-type template parameter, because it doesn't say what happens for them. Not to be done editorially, but a cleanup would be nice.

@jensmaurer jensmaurer added cwg Issue must be reviewed by CWG. and removed decision-required A decision of the editorial group (or the Project Editor) is required. labels Jul 16, 2019
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