http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60679
Bug ID: 60679
Summary: class specialization not instantiated even though it
is a better match than the primary template
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: filip.roseen at gmail dot com
Created attachment 32463
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=32463&action=edit
testcase.cpp
template<int...> struct A { }; // (A)
template<char X, char Y>
struct A<X, Y> { typedef int type; }; // (B)
int main () {
(void) A<0, 0>::type { };
}
-------------------------------------------------------------------------------
testcase.cpp: In function ‘int main()’:
testcase.cpp:7:10: error: ‘type’ is not a member of ‘A<0, 0>’
(void) A<0, 0>::type { };
^
-------------------------------------------------------------------------------
Note: `clang` correctly accepts `testcase.cpp`.
-------------------------------------------------------------------------------
This is how it should look, but gcc fails on step 4);
1. first our primary template `(A)` is looked up, and our template
arguments are deduced from those specified for this primary template
2. we then look for specializations, `(B)` should be found
3. `(B)` is more specialized than our primary template, proceed
4. `(B)` should be selected if no narrowing-conversion applies to
instantiating it, which is true; `int { 0 }` fits inside `char`
Note: A non-narrowing conversion can be proved since `0` is a
constant-expression and can fit inside `char`, see
[dcl.init.list]p7
5. `(B)` is the best candidate, instantiate it
-------------------------------------------------------------------------------
[temp.class.spec.match]p4:
> The templates arguments of a specializaton are deduced from the arguments
> of the primary template.
[temp.class.spec]p6 states the following:
> Partial specializations declarations themselves are not found by name
> lookup. Rather, when the primary template name is used, any
> previously-declared partial specializations of the primary template
> are also considered.
-------------------------------------------------------------------------------
