[Bug libstdc++/86751] [6/7/8 Regression] Ambiguous operator= overload for std::pair<T1, T2>

redi at gcc dot gnu.org gcc-bugzilla@gcc.gnu.org
Wed Oct 31 12:29:00 GMT 2018


--- Comment #10 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Author: redi
Date: Wed Oct 31 12:29:02 2018
New Revision: 265678

URL: https://gcc.gnu.org/viewcvs?rev=265678&root=gcc&view=rev
PR libstdc++/87822 fix layout change for nested std::pair

The introduction of the empty __pair_base base class for PR 86751
changed the layout of std::pair<std::pair<...>, ...>. The outer pair and
its first member both have a base class of the same type, which cannot
exist at the same address. This causes the first member to be at a
non-zero offset.

The solution is to make the base class depend on the template
parameters, so that each pair type has a different base class type,
which allows the base classes of the outer pair and its first member to
have the same address.

        PR libstdc++/87822
        * include/bits/stl_pair.h (__pair_base): Change to class template.
        (pair): Make base class type depend on template parameters.
        * testsuite/20_util/pair/87822.cc: New test.


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