Extern "apply(...)" and "merge(...)" methods in "StructPatch" and "UnionPatch"

Summary: They are expensive to build, let's explicitly instantiate them.

Reviewed By: thedavekwon

Differential Revision: D72946822

fbshipit-source-id: b6f560d8fe06bb4b730dbddb691cdf2a90d3549e

Author: Mizuchi

thrift/lib/cpp2/op/detail/StructPatch.h

@@ -508,7 +508,7 @@ class BaseEnsurePatch : public BaseClearPatch<Patch, Derived> {
     }
   }
 
-  void apply(T& val) const { return customVisit(Applier{val}); }
+  void apply(T& val) const;
 
   /**
    * Returns a Thrift Patch instance corresponding to the (decoded) `SafePatch`.
@@ -770,6 +770,9 @@ class StructPatch : public BaseEnsurePatch<Patch, StructPatch<Patch>> {
   }
   /// @endcond
 
+  void merge(const StructPatch& patch);
+  void merge(StructPatch&& patch);
+
  private:
   using Base::data_;
 
@@ -844,6 +847,9 @@ class UnionPatch : public BaseEnsurePatch<Patch, UnionPatch<Patch>> {
   void assign(U&& val) {
     op::get<Id>(Base::resetAnd().assign().ensure()) = std::forward<U>(val);
   }
+
+  void merge(const UnionPatch& patch);
+  void merge(UnionPatch&& patch);
 };
 
 } // namespace apache::thrift::op::detail

thrift/lib/cpp2/op/detail/StructPatchImpl.h

@@ -37,4 +37,25 @@ auto BaseEnsurePatch<Patch, Derived>::patchImpl() -> patch_type& {
         "Field (id={}) is not patchable", folly::to_underlying(FieldId::value));
   }
 }
+
+template <class Patch, class Derived>
+void BaseEnsurePatch<Patch, Derived>::apply(T& val) const {
+  return customVisit(Applier{val});
+}
+template <class Patch>
+void StructPatch<Patch>::merge(const StructPatch& val) {
+  Base::merge(val);
+}
+template <class Patch>
+void StructPatch<Patch>::merge(StructPatch&& val) {
+  Base::merge(std::move(val));
+}
+template <class Patch>
+void UnionPatch<Patch>::merge(const UnionPatch& val) {
+  Base::merge(val);
+}
+template <class Patch>
+void UnionPatch<Patch>::merge(UnionPatch&& val) {
+  Base::merge(std::move(val));
+}
 } // namespace apache::thrift::op::detail