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/
