1// Copyright 2014 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef BASE_ANDROID_JNI_INT_WRAPPER_H_
6#define BASE_ANDROID_JNI_INT_WRAPPER_H_
7
8// Wrapper used to receive int when calling Java from native.
9// The wrapper disallows automatic conversion of long to int.
10// This is to avoid a common anti-pattern where a Java int is used
11// to receive a native pointer. Please use a Java long to receive
12// native pointers, so that the code works on both 32-bit and 64-bit
13// platforms. Note the wrapper allows other lossy conversions into
14// jint that could be consider anti-patterns, such as from size_t.
15
16// Checking is only done in debugging builds.
17
18#ifdef NDEBUG
19
20typedef jint JniIntWrapper;
21
22// This inline is sufficiently trivial that it does not change the
23// final code generated by g++.
24inline jint as_jint(JniIntWrapper wrapper) {
25  return wrapper;
26}
27
28#else
29
30class JniIntWrapper {
31 public:
32  JniIntWrapper() : i_(0) {}
33  JniIntWrapper(int i) : i_(i) {}
34  JniIntWrapper(const JniIntWrapper& ji) : i_(ji.i_) {}
35  template <class T> JniIntWrapper(const T& t) : i_(t) {}
36  jint as_jint() const { return i_; }
37 private:
38  // If you get an "is private" error at the line below it is because you used
39  // an implicit conversion to convert a long to an int when calling Java.
40  // We disallow this, as a common anti-pattern allows converting a native
41  // pointer (intptr_t) to a Java int. Please use a Java long to represent
42  // a native pointer. If you want a lossy conversion, please use an
43  // explicit conversion in your C++ code. Note an error is only seen when
44  // compiling on a 64-bit platform, as intptr_t is indistinguishable from
45  // int on 32-bit platforms.
46  JniIntWrapper(long);
47  jint i_;
48};
49
50inline jint as_jint(const JniIntWrapper& wrapper) {
51  return wrapper.as_jint();
52}
53
54#endif  // NDEBUG
55
56#endif  // BASE_ANDROID_JNI_INT_WRAPPER_H_
57