[libcxx-dev] Unqualified name use causes ambiguity through ADL

Marcin Zalewski via libcxx-dev libcxx-dev at lists.llvm.org
Tue Oct 8 21:39:31 PDT 2019

I have a library that redefines forward_as_tuple in its namespace, along
with some concrete types. This causes the problem with the following code:


Here, forward_as_tuple is being called unqualified, and ADL kicks in. ADL
finds the definition of forward_as_tuple in the library that I am using,
and I get ambiguity.

It definitely can be argued that the library I am using makes a dangerous
choice by sticking concrete types into the same namespace as the template
forward_as_tuple, but it does. My question is why libc++ calls
forward_as_tuple unqualified rather than std::forward_as_tuple. Is this a
bug, or is there a good reason for this?

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