https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105518
Bug ID: 105518
Summary: [rejects valid] nested lambda using an outer type
alias fails with constexpr integer in that alias
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: leventyilmaz at gmail dot com
Target Milestone: ---
The following valid code is fails to compile.
https://godbolt.org/z/v1sd9snGx
// Simple run-time to compile-time integer conversion:
template<class F>
auto toStatic(int i, F f) {
switch(i) {
case 0: return f( std::integral_constant<int, 0>{} );
case 1: return f( std::integral_constant<int, 1>{} );
case 2: return f( std::integral_constant<int, 2>{} );
default: assert("too big");
}
}
// example types:
struct Base {
virtual void show() const = 0;
};
template <size_t I> struct F {
template <size_t J> struct K : Base {
void show() const override {
std::cout << I << " " << J << std::endl;
}
};
};
// nested lambda complains "I" is not captured
// even though it is only being used at compile-time
void show(int i, int j) {
return toStatic(i, [j](auto I) {
using A = F<I>;
// using A = F<decltype(I)::value>; // this works
return toStatic(j, [](auto J) {
using impl = typename A::template K<J>;
impl{}.show();
});
});
}
source>:32:19: error: 'I' is not captured
32 | using impl = typename A::template K<J>;
| ^~~~
