Allow implicit conversion from Orphan<T> to…

Allow implicit conversion from Orphan<T> to Orphan<DynamicStruct/DynamicList/DynamicCapability> where applicable.

c++/src/capnp/capability-test.c++

@@ -561,6 +561,10 @@ TEST(Capability, ObjectsAndOrphans) {
   EXPECT_TRUE(orphan == nullptr);
 
   verifyClient(request.getCap(), loop, callCount2);
+
+  Orphan<DynamicCapability> dynamicOrphan2 = request.disownCap();
+  verifyClient(dynamicOrphan2.get(), loop, callCount2);
+  verifyClient(dynamicOrphan2.getReader(), loop, callCount2);
 }
 
 TEST(Capability, Lists) {

c++/src/capnp/dynamic.h

@@ -784,6 +784,9 @@ public:
   Orphan(Orphan&&) = default;
   Orphan& operator=(Orphan&&) = default;
 
+  template <typename T, typename = kj::EnableIf<kind<T>() == Kind::STRUCT>>
+  inline Orphan(Orphan<T>&& other): schema(Schema::from<T>()), builder(kj::mv(other.builder)) {}
+
   DynamicStruct::Builder get();
   DynamicStruct::Reader getReader() const;
 
@@ -820,6 +823,9 @@ public:
   Orphan(Orphan&&) = default;
   Orphan& operator=(Orphan&&) = default;
 
+  template <typename T, typename = kj::EnableIf<kind<T>() == Kind::LIST>>
+  inline Orphan(Orphan<T>&& other): schema(Schema::from<T>()), builder(kj::mv(other.builder)) {}
+
   DynamicList::Builder get();
   DynamicList::Reader getReader() const;
 
@@ -855,6 +861,9 @@ public:
   Orphan(Orphan&&) = default;
   Orphan& operator=(Orphan&&) = default;
 
+  template <typename T, typename = kj::EnableIf<kind<T>() == Kind::INTERFACE>>
+  inline Orphan(Orphan<T>&& other): schema(Schema::from<T>()), builder(kj::mv(other.builder)) {}
+
   DynamicCapability::Client get();
   DynamicCapability::Client getReader() const;
 

c++/src/capnp/orphan-test.c++

@@ -332,6 +332,11 @@ TEST(Orphans, DynamicStruct) {
   EXPECT_TRUE(orphan == nullptr);
   EXPECT_TRUE(root.hasObjectField());
   checkTestMessage(root.asReader().getObjectField().getAs<TestAllTypes>());
+
+  Orphan<DynamicStruct> orphan2 = root.getObjectField().disownAs<TestAllTypes>();
+  EXPECT_FALSE(orphan2 == nullptr);
+  EXPECT_TRUE(orphan2.get().getSchema() == Schema::from<TestAllTypes>());
+  checkDynamicTestMessage(orphan2.getReader());
 }
 
 TEST(Orphans, DynamicList) {
@@ -352,6 +357,10 @@ TEST(Orphans, DynamicList) {
   EXPECT_TRUE(orphan == nullptr);
   EXPECT_TRUE(root.hasObjectField());
   checkList(root.asReader().getObjectField().getAs<List<uint32_t>>(), {12u, 34u, 56u});
+
+  Orphan<DynamicList> orphan2 = root.getObjectField().disownAs<List<uint32_t>>();
+  EXPECT_FALSE(orphan2 == nullptr);
+  checkList<uint32_t>(orphan2.getReader(), {12, 34, 56});
 }
 
 TEST(Orphans, DynamicStructList) {