cpp_variant.h

// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

/*
  This file contains the declaration for CppVariant, a type used by C++ classes
  that are to be bound to JavaScript objects.

  CppVariant exists primarily as an interface between C++ callers and the
  corresponding NPVariant type.  CppVariant also provides a number of
  convenience constructors and accessors, so that the NPVariantType values
  don't need to be exposed, and a destructor to free any memory allocated for
  string values.

  For a usage example, see cpp_binding_example.{h|cc}.
*/

#ifndef WEBKIT_RENDERER_CPP_VARIANT_H__
#define WEBKIT_RENDERER_CPP_VARIANT_H__

#include <string>
#include <vector>

#include "base/basictypes.h"
#include "third_party/npapi/bindings/npruntime.h"
#include "webkit/renderer/webkit_renderer_export.h"

namespace webkit_glue {

class WEBKIT_RENDERER_EXPORT CppVariant : public NPVariant {
 public:
  CppVariant();
  ~CppVariant();
  void SetNull();
  void Set(bool value);
  void Set(int32_t value);
  void Set(double value);

  // Note that setting a CppVariant to a string value involves copying the
  // string data, which must be freed with a call to FreeData() when the
  // CppVariant is set to a different value or is no longer needed.  Normally
  // this is handled by the other Set() methods and by the destructor.
  void Set(const char* value);  // Must be a null-terminated string.
  void Set(const std::string& value);
  void Set(const NPString& new_value);
  void Set(const NPVariant& new_value);

  // Note that setting a CppVariant to an NPObject involves ref-counting
  // the actual object. FreeData() should only be called if the CppVariant
  // is no longer needed. The other Set() methods handle this internally.
  // Also, the object's NPClass is expected to be a static object: neither
  // the NP runtime nor CPPVariant will ever free it.
  void Set(NPObject* new_value);

  // These three methods all perform deep copies of any string data.  This
  // allows local CppVariants to be released by the destructor without
  // corrupting their sources. In performance-critical code, or when strings
  // are very long, avoid creating new CppVariants.
  // In case of NPObject as the data, the copying involves ref-counting
  // as opposed to deep-copying. The ref-counting ensures that sources don't
  // get corrupted when the copies get destroyed.
  void CopyToNPVariant(NPVariant* result) const;
  CppVariant& operator=(const CppVariant& original);
  CppVariant(const CppVariant& original);

  // Calls NPN_ReleaseVariantValue, which frees any string data
  // held by the object and sets its type to null.
  // In case of NPObject, the NPN_ReleaseVariantValue decrements
  // the ref-count (releases when ref-count becomes 0)
  void FreeData();

  // Compares this CppVariant's type and value to another's.  They must be
  // identical in both type and value to be considered equal.  For string and
  // object types, a deep comparison is performed; that is, the contents of the
  // strings, or the classes and refcounts of the objects, must be the same,
  // but they need not be the same pointers.
  bool isEqual(const CppVariant& other) const;

  // The value of a CppVariant may be read directly from its NPVariant (but
  // should only be set using one of the Set() methods above). Although the
  // type of a CppVariant is likewise public, it can be accessed through these
  // functions rather than directly if a caller wishes to avoid dependence on
  // the NPVariantType values.
  bool isBool() const { return (type == NPVariantType_Bool); }
  bool isInt32() const { return (type == NPVariantType_Int32); }
  bool isDouble() const { return (type == NPVariantType_Double); }
  bool isNumber() const { return (isInt32() || isDouble()); }
  bool isString() const { return (type == NPVariantType_String); }
  bool isVoid() const { return (type == NPVariantType_Void); }
  bool isNull() const { return (type == NPVariantType_Null); }
  bool isEmpty() const { return (isVoid() || isNull()); }
  bool isObject() const { return (type == NPVariantType_Object); }

  // Converters.  The CppVariant must be of a type convertible to these values.
  // For example, ToInt32() works only if isNumber() is true.
  std::string ToString() const;
  int32_t ToInt32() const;
  double ToDouble() const;
  bool ToBoolean() const;
  // Returns a vector of CppVariant for the specified variant. This should only
  // be called on an Object. If the object has no "length" property an empty
  // vector is returned.
  std::vector<CppVariant> ToVector() const;

  // Invoke method of the given name on an object with the supplied arguments.
  // The first argument should be the object on which the method is to be
  // invoked.  Returns whether the method was successfully invoked.  If the
  // method was invoked successfully, any return value is stored in the
  // CppVariant specified by result.
  bool Invoke(const std::string& method, const CppVariant* args,
              uint32 arg_count, CppVariant& result) const;
};

}  // namespace webkit_glue

#endif  // WEBKIT_RENDERER_CPP_VARIANT_H__