https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70141
Bug ID: 70141
Summary: [6.0 regression] template parameter not deducible in
partial specialization of template inside template
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: kholdstare0.0 at gmail dot com
Target Milestone: ---
Created attachment 37899
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=37899&action=edit
Preprocessed source
The code below works on gcc 4.8, 5.2, and clang 3.6, but fails to compile on
gcc 6:
template <typename T>
struct outer
{
template <typename U>
struct inner
{
};
};
template <typename T>
struct is_inner_for
{
template <typename Whatever>
struct predicate
{
static constexpr bool value = false;
};
template <typename U>
struct predicate<typename outer<T>::template inner<U>>
{
static constexpr bool value = true;
};
};
static_assert(
is_inner_for<int>::template predicate<
outer<int>::inner<double>
>::value,
"Yay!"
);
The commandline:
g++ -std=c++1y -c main.cpp
Here is the error:
main.cpp:22:9: error: template parameters not deducible in partial
specialization:
struct predicate<typename outer<T>::template inner<U>> :
std::true_type
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
main.cpp:22:9: note: 'U'
main.cpp:26:1: error: static assertion failed: Yay!
static_assert(
^~~~~~~~~~~~~
Another thing I noticed is that *I get the error even if I don't use the
"is_inner_for" template*. It looks like some rule that gets applied before
template instantiation - maybe it's too strict...
