Bug 1142366 - Add an equivalent of std::make_pair for mozilla::Pair. r=waldo

mfbt/Pair.h

@@ -160,6 +160,10 @@ public:
     : Base(Forward<AArg>(aA), Forward<BArg>(aB))
   {}
 
+  Pair(Pair&& aOther)
+    : Base(Move(aOther.first()), Move(aOther.second()))
+  { }
+
   /** The A instance. */
   using Base::first;
   /** The B instance. */
@@ -179,6 +183,26 @@ Swap(Pair<A, B>& aX, Pair<A, B>& aY)
   aX.swap(aY);
 }
 
+/**
+ * MakePair allows you to construct a Pair instance using type inference. A call
+ * like this:
+ *
+ *   MakePair(Foo(), Bar())
+ *
+ * will return a Pair<Foo, Bar>.
+ */
+template<typename A, typename B>
+Pair<typename RemoveCV<typename RemoveReference<A>::Type>::Type,
+     typename RemoveCV<typename RemoveReference<B>::Type>::Type>
+MakePair(A&& aA, B&& aB)
+{
+  return
+    Pair<typename RemoveCV<typename RemoveReference<A>::Type>::Type,
+         typename RemoveCV<typename RemoveReference<B>::Type>::Type>(
+             Forward<A>(aA),
+             Forward<B>(aB));
+}
+
 } // namespace mozilla
 
 #endif /* mozilla_Pair_h */

mfbt/tests/TestPair.cpp

@@ -5,7 +5,10 @@
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "mozilla/Pair.h"
+#include "mozilla/TypeTraits.h"
 
+using mozilla::IsSame;
+using mozilla::MakePair;
 using mozilla::Pair;
 
 // Sizes aren't part of the guaranteed Pair interface, but we want to verify our
@@ -59,5 +62,18 @@ struct OtherEmpty : EmptyClass { explicit OtherEmpty(int aI) : EmptyClass(aI) {}
 int
 main()
 {
+  A a(0);
+  B b(0);
+  const A constA(0);
+  const B constB(0);
+
+  // Check that MakePair generates Pair objects of the correct types.
+  static_assert(IsSame<decltype(MakePair(A(0), B(0))), Pair<A, B>>::value,
+                "MakePair should strip rvalue references");
+  static_assert(IsSame<decltype(MakePair(a, b)), Pair<A, B>>::value,
+                "MakePair should strip lvalue references");
+  static_assert(IsSame<decltype(MakePair(constA, constB)), Pair<A, B>>::value,
+                "MakePair should strip CV-qualifiers");
+
   return 0;
 }