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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/52288] Trouble with operator?: and lambdas
Date: Thu, 16 Feb 2012 23:55:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D52288

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
           Severity|normal                      |enhancement

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-02-16 23=
:49:39 UTC ---
(In reply to comment #0)
> This code:
>=20
> int main(int argc, char** argv) {
>     bool b;
>     void* p =3D b ? [argc](int i){ return i; } :
>         [argc](int i){ return i; };
> return 0; }
>=20
> gets you this:
>=20
> s3:~/ootbc/personal/ivan$ g++ --std=3Dc++0x foo.cc
> foo.cc: In function =C3=A2int main(int, char**)=C3=A2:
> foo.cc:5:28: error: no match for ternary =C3=A2operator?:=C3=A2 in =C3=A2=
b ? {argc} : {argc}=C3=A2
>=20
> which is a poor.

What do you suggest instead?

> Meanwhile this code:
>=20
> int main(int argc, char** argv) {
>     bool b;
>     void* p =3D b ? &[argc](int i){ return i; } :
>         &[argc](int i){ return i; };
> return 0; }
>=20
> gets you this:
>=20
> s3:~/ootbc/personal/ivan$ g++ --std=3Dc++0x foo.cc
> foo.cc: In function =C3=A2int main(int, char**)=C3=A2:
> foo.cc:4:42: error: taking address of temporary [-fpermissive]
> foo.cc:5:29: error: taking address of temporary [-fpermissive]
> foo.cc:5:29: error: conditional expression between distinct pointer types
> =C3=A2main(int, char**)::<lambda(int)>*=C3=A2 and =C3=A2main(int, char**)=
::<lambda(int)>*=C3=A2
> lacks a cast
>=20
> which is even worse.

Why?  It's entirely accurate, you can't take the address of a lambda, and t=
he
two types are different and incompatible so can't be used as the second and
third operands of a conditional expression.