[libcxx-commits] [libcxx] [libc++] Make `flat_(multi)map`'s iterators require `operator<=>` (PR #131290)

[Mark de Wever via libcxx-commits]

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@@ -139,9 +141,12 @@ struct __key_value_iterator {
     return !(__x < __y);
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend auto operator<=>(const __key_value_iterator& __x, const __key_value_iterator& __y)
-    requires three_way_comparable<__key_iterator>
-  {
+  _LIBCPP_HIDE_FROM_ABI friend strong_ordering
+  operator<=>(const __key_value_iterator& __x, const __key_value_iterator& __y) {
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mordante wrote:

Based on [[[structure.specifications]](http://eel.is/c++draft/structure.specifications)/3.1](http://eel.is/c++draft/structure#specifications-3.1) it means "the conditions for the function's participation in overload resolution ([[over.match]](http://eel.is/c++draft/over.match))[.](http://eel.is/c++draft/structure#specifications-3.1.sentence-1)".

Note I did not validate whether or not there are issues in the specification in the Standard.

> I think we can just require the well-formedness of operator<=>.

What do you mean with require? a constraint or a mandate?


https://github.com/llvm/llvm-project/pull/131290