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From: "gcc@nicholas-schwab.de" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/98842] optional's spaceship operations generates
 wrong code when operator== is not present
Date: Tue, 26 Jan 2021 21:45:24 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98842

--- Comment #2 from gcc@nicholas-schwab.de ---
Created attachment 50063
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D50063&action=3Dedit
Patch operator<=3D>

The operator<=3D>(optional<_Tp>, _Up) is currently underconstrained. cf
http://eel.is/c++draft/optional.comp.with.t#25 . This patch fixes this by
adding the constraint three_way_comparable_with<_Tp> for _Up. Then in the
program that started this bug report=20

std::optional<expr>{} <=3D> std::optional<expr>{}=20

will not compile if operator=3D=3D(expr, expr) is not declared.=