[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Zhihao Yuan via Phabricator via cfe-commits]

lichray added a comment.

The standard hasn't allowed deducing any placeholder type without an initializer (10.1.7.4.1 [dcl.type.auto.deduct]/2) yet.

It's unclear to me what

  extern A x;

wants to archive.  Usually when people writing `extern` then expect an initializer to appear somewhere else, but with this declaration, defining

  A x = ...;

later may fail by resolving to a different type, which feels... interesting.


https://reviews.llvm.org/D38216