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From: "guille at cal dot berkeley.edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/67910] New: Two autos in a single function confuses the type system
Date: Fri, 09 Oct 2015 16:46:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 5.2.0
X-Bugzilla-Keywords:
X-Bugzilla-Severity: major
X-Bugzilla-Who: guille at cal dot berkeley.edu
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution:
X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67910

            Bug ID: 67910
           Summary: Two autos in a single function confuses the type
                    system
           Product: gcc
           Version: 5.2.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: guille at cal dot berkeley.edu
  Target Milestone: ---

The following code does not compile on 5.2.0:



struct A {};
struct B {};

static auto f(auto b) -> A { return A(); }

int main()
{
    A a = f(B());
    return 0;
}

whereas the following *does* compile:


struct A {};
struct B {};

static auto f(B b) -> A { return A(); }


int main()
{
    __attribute__((unused)) A a = f(B());
    return 0;
}


In the first (failing) case, the type system thinks that 'f' returns the same
type as the first auto *argument*, even though the return type is specified to
be 'A'.