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* [Bug c++/113563] New: Rejects capture of `this` in C++23 `this auto` lambda
@ 2024-01-23 17:38 arthur.j.odwyer at gmail dot com
2024-02-05 8:45 ` [Bug c++/113563] " de34 at live dot cn
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: arthur.j.odwyer at gmail dot com @ 2024-01-23 17:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113563
Bug ID: 113563
Summary: Rejects capture of `this` in C++23 `this auto` lambda
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: arthur.j.odwyer at gmail dot com
Target Milestone: ---
// https://godbolt.org/z/KWv8n6zEG
struct S {
int x_;
void f() {
[this](this auto) {
return this;
};
}
};
GCC trunk complains:
<source>:5:16: error: invalid use of 'this' in non-member function
5 | return this;
| ^~~~
The error also happens with
- [this](this auto&&) { return this; }
- [this](this auto) { return x; }
- [this](this auto) { f(); }
- [&](this auto) { return this; }
- [&](this auto) { return x; }
- [&](this auto) { f(); }
My understanding is that all of these lambdas should be well-formed, just as
long as the lambda's call operator is eventually instantiated (if it's ever
instantiated at all) with a type that satisfies [expr.prim.lambda.closure]/5,
i.e. is either the closure type itself or a class type derived from the closure
type.
Btw, I do like that GCC eagerly and SFINAE-friendlily rejects `[&](this T) {}`.
I hope fixing this bug doesn't require undoing that feature.
(By "SFINAE-friendly" I mean https://godbolt.org/z/fK4f13343 )
See also
https://quuxplusone.github.io/blog/2024/01/23/capturing-lambda-deducing-this/
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/113563] Rejects capture of `this` in C++23 `this auto` lambda
2024-01-23 17:38 [Bug c++/113563] New: Rejects capture of `this` in C++23 `this auto` lambda arthur.j.odwyer at gmail dot com
@ 2024-02-05 8:45 ` de34 at live dot cn
2024-02-07 14:56 ` ppalka at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: de34 at live dot cn @ 2024-02-05 8:45 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113563
Jiang An <de34 at live dot cn> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |de34 at live dot cn
--- Comment #1 from Jiang An <de34 at live dot cn> ---
(In reply to Arthur O'Dwyer from comment #0)
> Btw, I do like that GCC eagerly and SFINAE-friendlily rejects `[&](this T)
> {}`. I hope fixing this bug doesn't require undoing that feature.
> (By "SFINAE-friendly" I mean https://godbolt.org/z/fK4f13343 )
> See also
> https://quuxplusone.github.io/blog/2024/01/23/capturing-lambda-deducing-this/
Hmm... after reading CWG2672
(https://cplusplus.github.io/CWG/issues/2672.html), I think the
SFINAE-friendliness is actually required since the parameter list of a lambda
expression is in the immediate context (only the lambda body is excluded).
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/113563] Rejects capture of `this` in C++23 `this auto` lambda
2024-01-23 17:38 [Bug c++/113563] New: Rejects capture of `this` in C++23 `this auto` lambda arthur.j.odwyer at gmail dot com
2024-02-05 8:45 ` [Bug c++/113563] " de34 at live dot cn
@ 2024-02-07 14:56 ` ppalka at gcc dot gnu.org
2024-02-07 15:00 ` ppalka at gcc dot gnu.org
2024-03-06 19:56 ` ppalka at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: ppalka at gcc dot gnu.org @ 2024-02-07 14:56 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113563
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |hewillk at gmail dot com
--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
*** Bug 113810 has been marked as a duplicate of this bug. ***
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/113563] Rejects capture of `this` in C++23 `this auto` lambda
2024-01-23 17:38 [Bug c++/113563] New: Rejects capture of `this` in C++23 `this auto` lambda arthur.j.odwyer at gmail dot com
2024-02-05 8:45 ` [Bug c++/113563] " de34 at live dot cn
2024-02-07 14:56 ` ppalka at gcc dot gnu.org
@ 2024-02-07 15:00 ` ppalka at gcc dot gnu.org
2024-03-06 19:56 ` ppalka at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: ppalka at gcc dot gnu.org @ 2024-02-07 15:00 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113563
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ppalka at gcc dot gnu.org
--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
It works if we capture 'this' indirectly, e.g. via an init-capture:
struct S {
void f() {
[this_=this](this auto) {
return this_;
};
}
};
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/113563] Rejects capture of `this` in C++23 `this auto` lambda
2024-01-23 17:38 [Bug c++/113563] New: Rejects capture of `this` in C++23 `this auto` lambda arthur.j.odwyer at gmail dot com
` (2 preceding siblings ...)
2024-02-07 15:00 ` ppalka at gcc dot gnu.org
@ 2024-03-06 19:56 ` ppalka at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: ppalka at gcc dot gnu.org @ 2024-03-06 19:56 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113563
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rl.alt.accnt at gmail dot com
--- Comment #4 from Patrick Palka <ppalka at gcc dot gnu.org> ---
*** Bug 114257 has been marked as a duplicate of this bug. ***
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2024-03-06 19:56 UTC | newest]
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2024-01-23 17:38 [Bug c++/113563] New: Rejects capture of `this` in C++23 `this auto` lambda arthur.j.odwyer at gmail dot com
2024-02-05 8:45 ` [Bug c++/113563] " de34 at live dot cn
2024-02-07 14:56 ` ppalka at gcc dot gnu.org
2024-02-07 15:00 ` ppalka at gcc dot gnu.org
2024-03-06 19:56 ` ppalka at gcc dot gnu.org
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