Re: [PATCH] PR libstdc++/86963 Implement LWG 2729 constraints on tuple assignment

[Jonathan Wakely]

On 17/08/18 18:52 +0100, Jonathan Wakely wrote:

+  // The tag parameter ensures that in nested tuples each __tuple_base
+  // is a different type and can use the empty base-class optimisation.
+  template<typename _Tag>
+    class __tuple_base

Specifically, this would fail if __tuple_base was not a class
template:

static_assert(sizeof(tuple<tuple<int>>) == sizeof(int), "");

And also:

struct empty {};
static_assert(sizeof(tuple<tuple<empty>, tuple<empty>>) == 2, "");