base/android/jni_int_wrapper.h

   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
  20 typedef jint JniIntWrapper;
  21
  22 // This inline is sufficiently trivial that it does not change the
  23 // final code generated by g++.
  24 inline jint as_jint(JniIntWrapper wrapper) {
  25   return wrapper;
  26 }
  27
  28 #else
  29
  30 class 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
  50 inline 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_