https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85554
Bug ID: 85554
Summary: GCC does not instantiate template function when only
used as a function type
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: me at adhokshajmishraonline dot in
Target Milestone: ---
Proof of concept:
=================
template<typename T>
auto make_value(){
return T{};
}
template<typename F>
auto call(F func){
return func();
}
int main(){
auto result = call(make_value<double>);
return 0;
}
Compiling with G++
==================
╭─ adhokshajmishra@andromeda in /tmp
╰─➤ g++ --version
g++ (GCC) 7.3.1 20180406
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
╭─ adhokshajmishra@andromeda in /tmp
╰─➤ g++ test.cpp -o test -std=c++17
test.cpp: In function ‘int main()’:
test.cpp:12:42: error: no matching function for call to ‘call(<unresolved
overloaded function type>)’
auto result = call(make_value<double>);
^
test.cpp:7:6: note: candidate: template<class F> auto call(F)
auto call(F func){
^~~~
test.cpp:7:6: note: template argument deduction/substitution failed:
test.cpp:12:42: note: couldn't deduce template parameter ‘F’
auto result = call(make_value<double>);
^
Compiling with Clang: no error
As per [http://eel.is/c++draft/temp#inst-4.sentence-1], GCC seems to be wrong
here.
