ScopedLocalRef.h

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/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */
 
#pragma once
 
#include <jni.h>
#include <cstddef>
#include <type_traits>
 
namespace facebook::yoga::vanillajni {
 
template <typename T>
class ScopedLocalRef {
  static_assert(
      std::is_same<T, jclass>() || std::is_same<T, jobject>() ||
          std::is_same<T, jstring>() || std::is_same<T, jthrowable>() ||
          std::is_same<T, jbyteArray>() || std::is_same<T, jintArray>() ||
          std::is_same<T, jshortArray>() || std::is_same<T, jcharArray>() ||
          std::is_same<T, jlongArray>() || std::is_same<T, jfloatArray>() ||
          std::is_same<T, jdoubleArray>() || std::is_same<T, jobjectArray>() ||
          std::is_same<T, jbooleanArray>(),
      "ScopedLocalRef instantiated for invalid type");
 
 public:
  ScopedLocalRef(JNIEnv* env, T localRef) : mEnv(env), mLocalRef(localRef) {}
 
  explicit ScopedLocalRef(JNIEnv* env) : mEnv(env), mLocalRef(NULL) {}
 
  ScopedLocalRef(ScopedLocalRef&& s) noexcept
      : mEnv(s.mEnv), mLocalRef(s.release()) {}
 
  ScopedLocalRef& operator=(ScopedLocalRef&& s) noexcept {
    reset(s.release());
    mEnv = s.mEnv;
    return *this;
  }
 
  ~ScopedLocalRef() {
    reset();
  }
 
  void reset(T ptr = NULL) {
    if (ptr != mLocalRef) {
      if (mLocalRef != NULL) {
        mEnv->DeleteLocalRef(mLocalRef);
      }
      mLocalRef = ptr;
    }
  }
 
  T release() {
    T localRef = mLocalRef;
    mLocalRef = NULL;
    return localRef;
  }
 
  T get() const {
    return mLocalRef;
  }
 
  operator bool() const {
    return mLocalRef != NULL;
  }
 
  ScopedLocalRef(const ScopedLocalRef& ref) = delete;
  ScopedLocalRef& operator=(const ScopedLocalRef& other) = delete;
 
 private:
  JNIEnv* mEnv;
  T mLocalRef;
};
 
template <typename T>
ScopedLocalRef<T> make_local_ref(JNIEnv* env, T localRef) {
  return ScopedLocalRef<T>(env, localRef);
}
 
} // namespace facebook::yoga::vanillajni