Add as() functions to std::optional

Author: filipsajdak

include/cpp2util.h

@@ -675,6 +675,17 @@ auto optional_as(T&& t) -> auto {
     }
 }
 
+template< typename O, typename T >
+auto as(T&& t) -> auto
+    requires (
+        requires {O::value_type;}
+        && std::is_same_v<std::optional<typename O::value_type>,O>
+    )
+{
+    using C = typename O::value_type;
+    return cpp2::optional_as<C>(std::forward<T>(t));
+}
+
 //-------------------------------------------------------------------------------------------------------------
 //  std::variant is and as
 //