Issue 4125 - [emscripten] Convert filter classes to C++

compiled/intrusive_ptr.h

+// Parts of this code have been copied from boost/smart_ptr/intrusive_ptr.hpp.
+//
+//  Copyright (c) 2001, 2002 Peter Dimov
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#pragma once
+
+#include <algorithm>
+#include <type_traits>
+
+#include "debug.h"
+
+class ref_counted
+{
+public:
+  void AddRef()
+  {
+    mRefCount++;
+  }
+
+  void ReleaseRef()
+  {
+    assert(mRefCount > 0, u"Unexpected zero or negative reference count"_str);
+    if (--mRefCount == 0)
+      delete this;
+  }
+
+protected:
+  ref_counted()
+      : mRefCount(1)
+  {
+  }
+
+  // We need this virtual destructor, otherwise the numerical value of
+  // a ref_counted pointer and the numerical value of a pointer to a derived
+  // class will no longer be identical - despite still pointing to the same
+  // object. So for example `(int)(Filter*)ptr - (int)(ref_counted*)ptr` will be
+  // four, something that presents an issue for our JavaScript bindings which
+  // don't know how to convert pointers between different types.
+  virtual ~ref_counted()
+  {
+    assert(mRefCount == 0, u"Destroying a ref-counted object with a non-zero reference count"_str);
+  }
+
+private:
+  int mRefCount;
+};
+
+template<typename T,
+    class = typename std::enable_if<std::is_base_of<ref_counted,T>::value>::type>
+class intrusive_ptr
+{
+public:
+  intrusive_ptr()
+      : mPointer(nullptr)
+  {
+  }
+
+  explicit intrusive_ptr(T* pointer)
+      : mPointer(pointer)
+  {
+    // Raw pointers always had their reference count increased by whatever gave
+    // us the pointer so we don't need to do it here.
+  }
+
+  intrusive_ptr(const intrusive_ptr& other)
+      : mPointer(other.mPointer)
+  {
+    if (mPointer)
+      mPointer->AddRef();
+  }
+
+  intrusive_ptr(intrusive_ptr&& other)
+      : mPointer(other.mPointer)
+  {
+    other.mPointer = nullptr;
+  }
+
+  ~intrusive_ptr()
+  {
+    if (mPointer)
+      mPointer->ReleaseRef();
+  }
+
+  intrusive_ptr& operator=(intrusive_ptr& other)
+  {
+    intrusive_ptr(other).swap(*this);
+    return *this;
+  }
+
+  intrusive_ptr& operator=(intrusive_ptr&& other)
+  {
+    intrusive_ptr(std::move(other)).swap(*this);
+    return *this;
+  }
+
+  intrusive_ptr& operator=(T* other)
+  {
+    intrusive_ptr(other).swap(*this);
+    return *this;
+  }
+
+  void reset()
+  {
+    intrusive_ptr().swap(*this);
+  }
+
+  void reset(T* other)
+  {
+    intrusive_ptr(other).swap(*this);
+  }
+
+  const T* get() const
+  {
+    return mPointer;
+  }
+
+  T* get()
+  {
+    return mPointer;
+  }
+
+  const T& operator*() const
+  {
+    return *mPointer;
+  }
+
+  T& operator*()
+  {
+    return *mPointer;
+  }
+
+  const T* operator->() const
+  {
+    return mPointer;
+  }
+
+  T* operator->()
+  {
+    return mPointer;
+  }
+
+  explicit operator bool() const
+  {
+    return mPointer != nullptr;
+  }
+
+  bool operator!() const
+  {
+    return mPointer == nullptr;
+  }
+
+  T* release()
+  {
+    T* result = mPointer;
+    mPointer = nullptr;
+    return result;
+  }
+
+  void swap(intrusive_ptr& other)
+  {
+    std::swap(mPointer, other.mPointer);
+  }
+
+private:
+  T* mPointer;
+};
+
+template<typename T, typename U>
+inline bool operator==(const intrusive_ptr<T>& a, const intrusive_ptr<U>& b)
+{
+  return a.get() == b.get();
+}
+
+template<typename T, typename U>
+inline bool operator!=(const intrusive_ptr<T>& a, const intrusive_ptr<U>& b)
+{
+  return a.get() != b.get();
+}
+
+template<typename T, typename U>
+inline bool operator==(const intrusive_ptr<T>& a, const U* b)
+{
+  return a.get() == b;
+}
+
+template<typename T, typename U>
+inline bool operator!=(const intrusive_ptr<T>& a, const U* b)
+{
+    return a.get() != b;
+}
+
+template<typename T, typename U>
+inline bool operator==(const T* a, const intrusive_ptr<U>& b)
+{
+  return a == b.get();
+}
+
+template<typename T, typename U>
+inline bool operator!=(const T* a, intrusive_ptr<U> const& b)
+{
+  return a != b.get();
+}