Consider the following example (godbolt):
template <typename T>
struct S {
S(int) {}
};
template <typename T>
void f(S<T>, T) {}
int main() {
f(1, 2);
}
Compiling it gives the following error:
<source>: In function 'int main()':
10 : <source>:10:11: error: no matching function for call to 'f(int, int)'
f(1, 2);
^
7 : <source>:7:6: note: candidate: template<class T> void f(S<T>, T)
void f(S<T>, T) {}
^
7 : <source>:7:6: note: template argument deduction/substitution failed:
10 : <source>:10:11: note: mismatched types 'S<T>' and 'int'
f(1, 2);
^
Making S a non-template makes the example compile.
Why doesn't this code compile despite an implicit conversion from int to S<T>?