[libcxx-commits] [libcxx] [libc++] Implement LWG4257: Stream insertion for chrono local_time should be constrained (PR #230811)

[A. Jiang via libcxx-commits]

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@@ -215,8 +216,38 @@ static void test_ja_JP() {
              std::chrono::duration<long long, std::ratio<1, 100>>{12'345'678'9010}}) == SV("2009-02-13 23:31:30.10"));
 }
 
+template <class CharT, class T>
+concept is_ostreamable = requires(std::basic_ostream<CharT>& os, T const& val) {
+  { os << val };
+};
+
 template <class CharT>
 static void test() {
+  // Test local_time's constraints:
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frederick-vs-ja wrote:

I think it's more consistent to call it in `test`. As we're testing `char` and `wchar_t` versions, I think it's fine to introduce a function template for this.

https://github.com/llvm/llvm-project/pull/230811