Maybe::emplace() should return the newly-constructed value so that you don't…

Maybe::emplace() should return the newly-constructed value so that you don't have to immediately KJ_ASSERT_NONNULL it.

c++/src/kj/common.h

@@ -810,13 +810,14 @@ public:
   inline operator const T*() const { return isSet ? &value : nullptr; }
 
   template <typename... Params>
-  inline void emplace(Params&&... params) {
+  inline T& emplace(Params&&... params) {
     if (isSet) {
       isSet = false;
       dtor(value);
     }
     ctor(value, kj::fwd<Params>(params)...);
     isSet = true;
+    return value;
   }
 
 private:  // internal interface used by friends only
@@ -982,11 +983,12 @@ public:
   Maybe(decltype(nullptr)) noexcept: ptr(nullptr) {}
 
   template <typename... Params>
-  inline void emplace(Params&&... params) {
+  inline T& emplace(Params&&... params) {
     // Replace this Maybe's content with a new value constructed by passing the given parametrs to
     // T's constructor. This can be used to initialize a Maybe without copying or even moving a T.
+    // Returns a reference to the newly-constructed value.
 
-    ptr.emplace(kj::fwd<Params>(params)...);
+    return ptr.emplace(kj::fwd<Params>(params)...);
   }
 
   inline Maybe& operator=(Maybe&& other) { ptr = kj::mv(other.ptr); return *this; }