[dcl.type.decltype] What type does decltype of a splice specialization denote?

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
42/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Quiet
Tech stack
cpp
Domain
compilers

Research direction

Read [dcl.type.decltype] alongside [expr.prim.splice] and [dcl.type.splice], and review P2996R13. Trace how a template splice-specialization-specifier selects the variable-template specialization S, then determine what type decltype should denote. Done means the wording clearly defines the variable-template case without needing to resolve the separate function-template overload-set question.

Written by the indexing model from the issue text.

Description

Subclause: [dcl.type.decltype]

P2996R13 specifies decltype(E) for an unparenthesized splice expression as the type of the entity, object, or value designated by the splice-specifier of E.

For a template splice-specialization-specifier, however, the contained splice-specifier designates the template, while [expr.prim.splice] forms the selected variable-template specialization S from that template and the template arguments.

For example:

template<class T> T value;

using R = decltype(template [:^^value:]<int>);

I would expect R to be int, the declared type of value<int>, but the current decltype bullet appears to ask for the type of the variable template value, which does not have a type. Is there another rule that makes this case well-defined?

If not, should [dcl.type.decltype] distinguish this form and use the type of the selected specialization S, following the construction already used in [expr.prim.splice] and [dcl.type.splice]?

The function-template forms are a separate question because they denote overload sets. They do not need to be resolved in order to clarify the variable-template case above.

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