https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100720
Bug ID: 100720
Summary: inconsistent return type deduction behavior with user
defined conversion function
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: nickgray0 at brown dot edu
Target Milestone: ---
the following code compiles successfully:
auto f(auto);
template<typename = int>
struct A {
auto g() {
return f(0);
}
};
auto f(auto) {
if (true)
return 42;
else
return A{}.g();
}
auto main()->int {
f(123);
}
however if we rename A::g as a conversion function:
auto f(auto);
template<typename = int>
struct A {
operator auto() {
return f(0);
}
};
auto f(auto) {
if (true)
return 42;
else
return static_cast<int>(A{});
}
auto main()->int {
f(123);
}
it fails with the error: <source>: In instantiation of 'A<
<template-parameter-1-1> >::operator auto() [with <template-parameter-1-1> =
int]':
<source>:14:36: required from here
<source>:6:17: error: use of 'auto f(auto:1) [with auto:1 = int]' before
deduction of 'auto'
6 | return f(0);
| ~^~~
<source>: In function 'auto f(auto:1)':
<source>:14:16: error: invalid 'static_cast' from type 'A<int>' to type 'int'
14 | return static_cast<int>(A{});
| ^~~~~~~~~~~~~~~~~~~~~
ASM generation compiler returned: 1
