Defaulted VC++ workaround

internals/tests/testing/defaulted_test.cpp

@@ -23,4 +23,12 @@ auto defaulted_test = test([]() {
     dumpster_v1::zeroed<char *> x;
     verify(x == nullptr);
   }
+  {
+    dumpster_v1::zeroed<uint8_t> x;
+    dumpster_v1::zeroed<uint8_t> y = x;
+    y += 1;
+    x = y;
+    x = 2 * y + 1;
+    verify(3 == x);
+  }
 });

provides/include/dumpster_v1/defaulted.hpp

@@ -21,3 +21,10 @@ template <class Value, auto... defaults>
 dumpster_v1::defaulted<Value, defaults...>::operator Value &() {
   return value;
 }
+
+template <class Value, auto... defaults>
+template <class Forwardable>
+Value &dumpster_v1::defaulted<Value, defaults...>::
+operator=(Forwardable &&rhs) {
+  return value = std::forward<Forwardable>(rhs);
+}

provides/include/dumpster_v1/synopsis.hpp

@@ -23,6 +23,9 @@ template <class Value, auto... defaults> struct defaulted {
   /// Implicit conversion to reference for convenience.
   operator Value &();
 
+  /// Assigns given `rhs` to `value` member.
+  template <class Forwardable> Value &operator=(Forwardable &&rhs);
+
   /// The value is directly accessible as there is no reason to hide it.
   Value value;
 };