ui/base/class_property.h

// Copyright 2017 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.

#ifndef UI_BASE_CLASS_PROPERTY_H_
#define UI_BASE_CLASS_PROPERTY_H_

#include <stdint.h>

#include <map>
#include <set>

#include "base/time/time.h"
#include "ui/base/ui_base_export.h"
#include "ui/base/ui_base_types.h"

// This header should be included by code that defines ClassProperties.
//
// To define a new ClassProperty:
//
//  #include "foo/foo_export.h"
//  #include "ui/base/class_property.h"
//
//  DEFINE_EXPORTED_UI_CLASS_PROPERTY_TYPE(FOO_EXPORT, MyType)
//  namespace foo {
//    // Use this to define an exported property that is primitive,
//    // or a pointer you don't want automatically deleted.
//    DEFINE_UI_CLASS_PROPERTY_KEY(MyType, kMyKey, MyDefault)
//
//    // Use this to define an exported property whose value is a heap
//    // allocated object, and has to be owned and freed by the class.
//    DEFINE_OWNED_UI_CLASS_PROPERTY_KEY(gfx::Rect, kRestoreBoundsKey, nullptr)
//
//  }  // foo namespace
//
// To define a new type used for ClassProperty.
//
//  // outside all namespaces:
//  DEFINE_EXPORTED_UI_CLASS_PROPERTY_TYPE(FOO_EXPORT, MyType)
//
// If a property type is not exported, use
// DEFINE_UI_CLASS_PROPERTY_TYPE(MyType) which is a shorthand for
// DEFINE_EXPORTED_UI_CLASS_PROPERTY_TYPE(, MyType).
//
// If the properties are used outside the file where they are defined
// their accessor methods should also be declared in a suitable header
// using DECLARE_EXPORTED_UI_CLASS_PROPERTY_TYPE(FOO_EXPORT, MyType)

namespace ui {

// Type of a function to delete a property that this window owns.
using PropertyDeallocator = void(*)(int64_t value);

template<typename T>
struct ClassProperty {
  T default_value;
  const char* name;
  PropertyDeallocator deallocator;
};

namespace subtle {

class PropertyHelper;

}

class UI_BASE_EXPORT PropertyHandler {
 public:
  PropertyHandler();
  PropertyHandler(PropertyHandler&& other);
  virtual ~PropertyHandler();
  PropertyHandler& operator=(PropertyHandler&& rhs) = default;

  // Takes the ownership of all the properties in |other|, overwriting any
  // similarly-keyed existing properties without affecting existing ones with
  // different keys.
  void AcquireAllPropertiesFrom(PropertyHandler&& other);

  // Sets the |value| of the given class |property|. Setting to the default
  // value (e.g., NULL) removes the property. The lifetime of objects set as
  // values of unowned properties is managed by the caller (owned properties are
  // freed when they are overwritten or cleared).
  template<typename T>
  void SetProperty(const ClassProperty<T>* property, T value);

  // Sets the |value| of the given class |property|, which must be an owned
  // property of pointer type. The property will be assigned a copy of |value|;
  // if no property object exists one will be allocated. T must support copy
  // construction and assignment.
  template <typename T>
  void SetProperty(const ClassProperty<T*>* property, const T& value);

  // Sets the |value| of the given class |property|, which must be an owned
  // property and of pointer type. The property will be move-assigned or move-
  // constructed from |value|; if no property object exists one will be
  // allocated. T must support at least copy (and ideally move) semantics.
  template <typename T>
  void SetProperty(const ClassProperty<T*>* property, T&& value);

  // Returns the value of the given class |property|.  Returns the
  // property-specific default value if the property was not previously set.
  template<typename T>
  T GetProperty(const ClassProperty<T>* property) const;

  // Sets the |property| to its default value. Useful for avoiding a cast when
  // setting to NULL.
  template<typename T>
  void ClearProperty(const ClassProperty<T>* property);

  // Returns the value of all properties with a non-default value.
  std::set<const void*> GetAllPropertyKeys() const;

 protected:
  friend class subtle::PropertyHelper;

  virtual void AfterPropertyChange(const void* key, int64_t old_value) {}
  void ClearProperties();

  // Called by the public {Set,Get,Clear}Property functions.
  int64_t SetPropertyInternal(const void* key,
                              const char* name,
                              PropertyDeallocator deallocator,
                              int64_t value,
                              int64_t default_value);
  int64_t GetPropertyInternal(const void* key, int64_t default_value) const;

 private:
  // Value struct to keep the name and deallocator for this property.
  // Key cannot be used for this purpose because it can be char* or
  // ClassProperty<>.
  struct Value {
    const char* name;
    int64_t value;
    PropertyDeallocator deallocator;
  };

  std::map<const void*, Value> prop_map_;
};

namespace {

// No single new-style cast works for every conversion to/from int64_t, so we
// need this helper class. A third specialization is needed for bool because
// MSVC warning C4800 (forcing value to bool) is not suppressed by an explicit
// cast (!).
template<typename T>
class ClassPropertyCaster {
 public:
  static int64_t ToInt64(T x) { return static_cast<int64_t>(x); }
  static T FromInt64(int64_t x) { return static_cast<T>(x); }
};
template<typename T>
class ClassPropertyCaster<T*> {
 public:
  static int64_t ToInt64(T* x) { return reinterpret_cast<int64_t>(x); }
  static T* FromInt64(int64_t x) { return reinterpret_cast<T*>(x); }
};
template<>
class ClassPropertyCaster<bool> {
 public:
  static int64_t ToInt64(bool x) { return static_cast<int64_t>(x); }
  static bool FromInt64(int64_t x) { return x != 0; }
};
template <>
class ClassPropertyCaster<base::TimeDelta> {
 public:
  static int64_t ToInt64(base::TimeDelta x) { return x.InMicroseconds(); }
  static base::TimeDelta FromInt64(int64_t x) {
    return base::TimeDelta::FromMicroseconds(x);
  }
};

}  // namespace

namespace subtle {

class UI_BASE_EXPORT PropertyHelper {
 public:
  template<typename T>
  static void Set(::ui::PropertyHandler* handler,
                  const ::ui::ClassProperty<T>* property, T value) {
    int64_t old = handler->SetPropertyInternal(
        property, property->name,
        value == property->default_value ? nullptr : property->deallocator,
        ClassPropertyCaster<T>::ToInt64(value),
        ClassPropertyCaster<T>::ToInt64(property->default_value));
    if (property->deallocator &&
        old != ClassPropertyCaster<T>::ToInt64(property->default_value)) {
      (*property->deallocator)(old);
    }
  }
  template<typename T>
  static T Get(const ::ui::PropertyHandler* handler,
               const ::ui::ClassProperty<T>* property) {
    return ClassPropertyCaster<T>::FromInt64(handler->GetPropertyInternal(
        property, ClassPropertyCaster<T>::ToInt64(property->default_value)));
  }
  template<typename T>
  static void Clear(::ui::PropertyHandler* handler,
                    const ::ui::ClassProperty<T>* property) {
    handler->SetProperty(property, property->default_value);
  }
};

}  // namespace subtle

// Template implementation is necessary in the .h file unless we want to break
// [DECLARE|DEFINE]_EXPORTED_UI_CLASS_PROPERTY_TYPE() below into different
// macros for owned and unowned properties; implementing them as pure templates
// makes them nearly impossible to implement or use incorrectly at the cost of a
// small amount of code duplication across libraries.

template <typename T>
void PropertyHandler::SetProperty(const ClassProperty<T*>* property,
                                  const T& value) {
  // Prevent additional heap allocation if possible.
  T* const old = GetProperty(property);
  if (old) {
    T temp(*old);
    *old = value;
    AfterPropertyChange(property, reinterpret_cast<int64_t>(&temp));
  } else {
    SetProperty(property, new T(value));
  }
}

template <typename T>
void PropertyHandler::SetProperty(const ClassProperty<T*>* property,
                                  T&& value) {
  // Prevent additional heap allocation if possible.
  T* const old = GetProperty(property);
  if (old) {
    T temp(std::move(*old));
    *old = std::forward<T>(value);
    AfterPropertyChange(property, reinterpret_cast<int64_t>(&temp));
  } else {
    SetProperty(property, new T(std::forward<T>(value)));
  }
}

}  // namespace ui

// Macros to declare the property getter/setter template functions.
#define DECLARE_EXPORTED_UI_CLASS_PROPERTY_TYPE(EXPORT, T)                   \
  namespace ui {                                                             \
  template <>                                                                \
  EXPORT void PropertyHandler::SetProperty(const ClassProperty<T>* property, \
                                           T value);                         \
  template <>                                                                \
  EXPORT T                                                                   \
  PropertyHandler::GetProperty(const ClassProperty<T>* property) const;      \
  template <>                                                                \
  EXPORT void PropertyHandler::ClearProperty(                                \
      const ClassProperty<T>* property);                                     \
  }  // namespace ui

// Macros to instantiate the property getter/setter template functions.
#define DEFINE_EXPORTED_UI_CLASS_PROPERTY_TYPE(EXPORT, T)                    \
  namespace ui {                                                             \
  template <>                                                                \
  EXPORT void PropertyHandler::SetProperty(const ClassProperty<T>* property, \
                                           T value) {                        \
    subtle::PropertyHelper::Set<T>(this, property, value);                   \
  }                                                                          \
  template <>                                                                \
  EXPORT T                                                                   \
  PropertyHandler::GetProperty(const ClassProperty<T>* property) const {     \
    return subtle::PropertyHelper::Get<T>(this, property);                   \
  }                                                                          \
  template <>                                                                \
  EXPORT void PropertyHandler::ClearProperty(                                \
      const ClassProperty<T>* property) {                                    \
    subtle::PropertyHelper::Clear<T>(this, property);                        \
  }                                                                          \
  }  // namespace ui

#define DEFINE_UI_CLASS_PROPERTY_TYPE(T) \
  DEFINE_EXPORTED_UI_CLASS_PROPERTY_TYPE(, T)

#define DEFINE_UI_CLASS_PROPERTY_KEY(TYPE, NAME, DEFAULT)                    \
  static_assert(sizeof(TYPE) <= sizeof(int64_t), "property type too large"); \
  const ::ui::ClassProperty<TYPE> NAME##_Value = {DEFAULT, #NAME, nullptr};  \
  const ::ui::ClassProperty<TYPE>* const NAME = &NAME##_Value;

#define DEFINE_OWNED_UI_CLASS_PROPERTY_KEY(TYPE, NAME, DEFAULT)         \
  namespace {                                                           \
  void Deallocator##NAME(int64_t p) {                                   \
    enum { type_must_be_complete = sizeof(TYPE) };                      \
    delete ::ui::ClassPropertyCaster<TYPE*>::FromInt64(p);              \
  }                                                                     \
  const ::ui::ClassProperty<TYPE*> NAME##_Value = {DEFAULT, #NAME,      \
                                                   &Deallocator##NAME}; \
  } /* namespace */                                                     \
  const ::ui::ClassProperty<TYPE*>* const NAME = &NAME##_Value;

#endif  // UI_BASE_CLASS_PROPERTY_H_