commit 48b50b5ac0b2f36d6b2f00c51862fe5461119eca
Author: Jason Merrill <jason@redhat.com>
Date: Thu Feb 14 12:00:30 2013 -0500
PR c++/55220
* pt.c (unify): A pack expansion that is not the last template
argument makes the entire template argument list non-deduced.
@@ -16548,6 +16548,14 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
&& PACK_EXPANSION_P (TREE_VEC_ELT (parmvec, len - 1)))
parm_variadic_p = 1;
+ for (i = 0; i < len - parm_variadic_p; ++i)
+ /* If the template argument list of P contains a pack
+ expansion that is not the last template argument, the
+ entire template argument list is a non-deduced
+ context. */
+ if (PACK_EXPANSION_P (TREE_VEC_ELT (parmvec, i)))
+ return unify_success (explain_p);
+
if (TREE_VEC_LENGTH (argvec) < len - parm_variadic_p)
return unify_too_few_arguments (explain_p,
TREE_VEC_LENGTH (argvec), len);
new file mode 100644
@@ -0,0 +1,25 @@
+// PR c++/55220
+// { dg-do compile { target c++11 } }
+
+template <typename ...> struct something_like_tuple
+{
+
+};
+
+template <typename, typename> struct is_last
+{
+ static const bool value = false;
+};
+
+// Head is non-deducible, so this can't work as the user intended
+template <typename T, template <typename ...> class Tuple, typename ... Head>
+struct is_last<T, Tuple<Head ..., T>>
+{
+ static const bool value = true;
+};
+
+#define SA(X) static_assert (X, #X)
+
+typedef something_like_tuple<char, int, float> something_like_tuple_t;
+SA ((is_last<float, something_like_tuple_t>::value == false));
+SA ((is_last<int, something_like_tuple_t>::value == false));