Source/JavaScriptCore/API/JSManagedValue.h

/*
 * Copyright (C) 2013 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef JSManagedValue_h
#define JSManagedValue_h

#import <JavaScriptCore/JSBase.h>

#if JSC_OBJC_API_ENABLED

@class JSValue;
@class JSContext;

// JSManagedValue represents a "conditionally retained" JSValue. 
// "Conditionally retained" means that as long as either the JSManagedValue 
// JavaScript value is reachable through the JavaScript object graph
// or the JSManagedValue object is reachable through the external Objective-C 
// object graph as reported to the JSVirtualMachine using 
// addManagedReference:withOwner:, the corresponding JavaScript value will 
// be retained. However, if neither of these conditions are true, the 
// corresponding JSValue will be released and set to nil.
//
// The primary use case for JSManagedValue is for safely referencing JSValues 
// from the Objective-C heap. It is incorrect to store a JSValue into an 
// Objective-C heap object, as this can very easily create a reference cycle, 
// keeping the entire JSContext alive. 
#ifndef JSC_OBJC_API_AVAILABLE_MAC_OS_X_1080
NS_CLASS_AVAILABLE(10_9, NA)
#else
OBJC_VISIBLE
#endif
@interface JSManagedValue : NSObject

// Convenience method for creating JSManagedValues from JSValues.
+ (JSManagedValue *)managedValueWithValue:(JSValue *)value;

// Create a JSManagedValue.
- (id)initWithValue:(JSValue *)value;

// Get the JSValue to which this JSManagedValue refers. If the JavaScript value has been collected,
// this method returns nil.
- (JSValue *)value;

@end

#endif // JSC_OBJC_API_ENABLED

#endif // JSManagedValue_h