[committed] libstdc++: Simplify constraints for semiregular-box [LWG 3477]

[Jonathan Wakely via Gcc-patches]

libstdc++-v3/ChangeLog:

        * include/std/ranges (__box): Simplify constraints as per LWG 3477.

Tested powerpc64le-linux. Committed to trunk.


commit 00ffe730072f5e2e1923692163dc37db7b3784cb
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Mon Sep 7 20:09:17 2020

    libstdc++: Simplify constraints for semiregular-box [LWG 3477]
    
    libstdc++-v3/ChangeLog:
    
            * include/std/ranges (__box): Simplify constraints as per LWG 3477.

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 054ffe85d0f..23a04d61174 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -494,10 +494,12 @@ namespace ranges
 
        using std::optional<_Tp>::operator=;
 
+       // _GLIBCXX_RESOLVE_LIB_DEFECTS
+       // 3477. Simplify constraints for semiregular-box
        __box&
        operator=(const __box& __that)
        noexcept(is_nothrow_copy_constructible_v<_Tp>)
-       requires (!assignable_from<_Tp&, const _Tp&>)
+       requires (!copyable<_Tp>)
        {
          if ((bool)__that)
            this->emplace(*__that);
@@ -509,7 +511,7 @@ namespace ranges
        __box&
        operator=(__box&& __that)
        noexcept(is_nothrow_move_constructible_v<_Tp>)
-       requires (!assignable_from<_Tp&, _Tp>)
+       requires (!movable<_Tp>)
        {
          if ((bool)__that)
            this->emplace(std::move(*__that));