http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60177
Bug ID: 60177
Summary: Unable to deduce template base of derived class in
function template accepting a simple-template-id
Product: gcc
Version: 4.9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: filip.roseen at gmail dot com
template<class> struct Base { };
struct Derived : Base<void> { };
template<template<typename> class TT, typename T>
void func (TT<T>) { }
int main () {
func (Derived { });
}
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main.cpp: In function 'int main()':
main.cpp:9:20: error: no matching function for call to 'func(Derived)'
func (Derived { });
^
main.cpp:9:20: note: candidate is:
main.cpp:6:6: note: template<template<class> class TT, class T> void
func(TT<T>)
void func (TT<T>) { }
^
main.cpp:6:6: note: template argument deduction/substitution failed:
main.cpp:9:20: note: can't deduce a template for 'TT<T>' from non-template
type 'Derived'
func (Derived { });
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gcc rejects the snippet which is a violation of [temp.deduct.call]/4 (`clang`
and `msvc` accepts the code).
`TT<T>` is a `simple-template-id` and the standard says that if a derived type
is passed to such context it should be deduced to a suitable base of that
passed type.
Correct behavior is that the deduced template parameters for `func (Derived
{})` should be `TT = Base, T = void`.
