// Copyright (c) 2011 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 BASE_MAC_OBJC_PROPERTY_RELEASER_H_
#define BASE_MAC_OBJC_PROPERTY_RELEASER_H_
#import <Foundation/Foundation.h>
#include "base/base_export.h"
namespace base {
namespace mac {
// ObjCPropertyReleaser is a C++ class that can automatically release
// synthesized Objective-C properties marked "retain" or "copy". The expected
// use is to place an ObjCPropertyReleaser object within an Objective-C class
// definition. When built with the -fobjc-call-cxx-cdtors compiler option,
// the ObjCPropertyReleaser's destructor will be called when the Objective-C
// object that owns it is deallocated, and it will send a -release message to
// the instance variables backing the appropriate properties. If
// -fobjc-call-cxx-cdtors is not in use, ObjCPropertyReleaser's
// ReleaseProperties method can be called from -dealloc to achieve the same
// effect.
//
// Example usage:
//
// @interface AllaysIBF : NSObject {
// @private
// NSString* string_;
// NSMutableDictionary* dictionary_;
// NSString* notAProperty_;
// IBFDelegate* delegate_; // weak
//
// // It's recommended to put the class name into the property releaser's
// // instance variable name to gracefully handle subclassing, where
// // multiple classes in a hierarchy might want their own property
// // releasers.
// base::mac::ObjCPropertyReleaser propertyReleaser_AllaysIBF_;
// }
//
// @property(retain, nonatomic) NSString* string;
// @property(copy, nonatomic) NSMutableDictionary* dictionary;
// @property(assign, nonatomic) IBFDelegate* delegate;
// @property(retain, nonatomic) NSString* autoProp;
//
// @end // @interface AllaysIBF
//
// @implementation AllaysIBF
//
// @synthesize string = string_;
// @synthesize dictionary = dictionary_;
// @synthesize delegate = delegate_;
// @synthesize autoProp;
//
// - (id)init {
// if ((self = [super init])) {
// // Initialize with [AllaysIBF class]. Never use [self class] because
// // in the case of subclassing, it will return the most specific class
// // for |self|, which may not be the same as [AllaysIBF class]. This
// // would cause AllaysIBF's -.cxx_destruct or -dealloc to release
// // instance variables that only exist in subclasses, likely causing
// // mass disaster.
// propertyReleaser_AllaysIBF_.Init(self, [AllaysIBF class]);
// }
// return self;
// }
//
// @end // @implementation AllaysIBF
//
// When an instance of AllaysIBF is deallocated, the ObjCPropertyReleaser will
// send a -release message to string_, dictionary_, and the compiler-created
// autoProp instance variables. No -release will be sent to delegate_ as it
// is marked "assign" and not "retain" or "copy". No -release will be sent to
// notAProperty_ because it doesn't correspond to any declared @property.
//
// Another way of doing this would be to provide a base class that others can
// inherit from, and to have the base class' -dealloc walk the property lists
// of all subclasses in an object to send the -release messages. Since this
// involves a base reaching into its subclasses, it's deemed scary, so don't
// do it. ObjCPropertyReleaser's design ensures that the property releaser
// will only operate on instance variables in the immediate object in which
// the property releaser is placed.
class BASE_EXPORT ObjCPropertyReleaser {
public:
// ObjCPropertyReleaser can only be owned by an Objective-C object, so its
// memory is always guaranteed to be 0-initialized. Not defining the default
// constructor can prevent an otherwise no-op -.cxx_construct method from
// showing up in Objective-C classes that contain a ObjCPropertyReleaser.
// Upon destruction (expected to occur from an Objective-C object's
// -.cxx_destruct method), release all properties.
~ObjCPropertyReleaser() {
ReleaseProperties();
}
// Initialize this object so that it's armed to release the properties of
// object |object|, which must be of type |classy|. The class argument must
// be supplied separately and cannot be gleaned from the object's own type
// because an object will allays identify itself as the most-specific type
// that describes it, but the ObjCPropertyReleaser needs to know which class
// type in the class hierarchy it's responsible for releasing properties
// for. For the same reason, Init must be called with a |classy| argument
// initialized using a +class (class) method such as [MyClass class], and
// never a -class (instance) method such as [self class].
//
// -.cxx_construct can only call the default constructor, but
// ObjCPropertyReleaser needs to know about the Objective-C object that owns
// it, so this can't be handled in a constructor, it needs to be a distinct
// Init method.
void Init(id object, Class classy);
// Release all of the properties in object_ defined in class_ as either
// "retain" or "copy" and with an identifiable backing instance variable.
// Properties must be synthesized to have identifiable instance variables.
void ReleaseProperties();
private:
id object_;
Class class_;
};
} // namespace mac
} // namespace base
#endif // BASE_MAC_OBJC_PROPERTY_RELEASER_H_