Deduction guides and variadic class templates with variadic template constructors – mismatched argument pack lengths

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To simplify your example further, it appears that GCC does not implement variadic template arguments in deduction guides:

https://wandbox.org/permlink/4YsacnW9wYcoceDH

I didn’t see any explicit mention of variadic templates in the wording for deduction guides in the standard or on cppreference.com. I see no interpretation of the standard that disallows this. Therefore I think this is a bug.

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