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POObjective-C - Disadvantages to Bridging With C++?
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  1. POObjective-C - Disadvantages to Bridging With C++?
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    copied!<p>So, I was bored today, and decide to mess with C++/Obj-C interpolation, and I found a way to create a very interesting setup.</p> <pre><code>@protocol NSCPPObj &lt;NSObject&gt; -(id) init; -(id) initWithInt:(int) value; -(int) somethingThatReturnsAValue; -(void) doSomething; @end class NSCPPObj : objc_object { public: static Class cls(); int iVar; NSCPPObj(); NSCPPObj(int); int somethingThatReturnsAValue(); void doSomething(); }; </code></pre> <p>As you can see, the interface is quite straightforward, and easy to understand. We create two (almost) identical interfaces, one for a C++ object, and another for a Obj-C protocol.</p> <p>Now, I found a way to implement this, but brace yourself, this gets ugly:</p> <pre><code>// NSCPPObj.mm #import &lt;objc/runtime.h&gt; #import &lt;iostream&gt; #import "NSCPPObject.h" Class NSCPPObj_class = nil; __attribute__((constructor)) static void initialize() { NSCPPObj_class = objc_allocateClassPair([NSObject class], "NSCPPObj", 0); class_addMethod(NSCPPObj_class-&gt;isa, @selector(alloc), imp_implementationWithBlock(^(id self) { return class_createInstance(NSCPPObj_class, sizeof(struct NSCPPObj)); }), "@@:"); class_addMethod(NSCPPObj_class, @selector(init), imp_implementationWithBlock(^(id self) { return self; }), "@@:"); class_addMethod(NSCPPObj_class, @selector(initWithInt:), imp_implementationWithBlock(^(id self, int value) { ((struct NSCPPObj *) self)-&gt;iVar = value; return self; }), "@@:i"); class_addMethod(NSCPPObj_class, @selector(doSomething), imp_implementationWithBlock(^(id self) { ((struct NSCPPObj *) self)-&gt;doSomething(); }), "v@:"); class_addMethod(NSCPPObj_class, @selector(somethingThatReturnsAValue), imp_implementationWithBlock(^(id self) { return ((struct NSCPPObj *) self)-&gt;somethingThatReturnsAValue(); }), "i@:"); objc_registerClassPair(NSCPPObj_class); } Class NSCPPObj::cls() { return NSCPPObj_class; } NSCPPObj::NSCPPObj() { this-&gt;isa = NSCPPObj_class; [((id&lt;NSCPPObj&gt;) this) init]; } NSCPPObj::NSCPPObj(int value) { this-&gt;isa = NSCPPObj_class; [((id&lt;NSCPPObj&gt;) this) initWithInt:value]; } void NSCPPObj::doSomething() { std::cout &lt;&lt; "Value Is: " &lt;&lt; [((id&lt;NSCPPObj&gt;) this) somethingThatReturnsAValue] &lt;&lt; std::endl; } int NSCPPObj::somethingThatReturnsAValue() { return iVar; } </code></pre> <p>I'll summarize what this does: </p> <ol> <li>Allocates a Class Pair</li> <li>Adds all class and instance methods to the object</li> <li>Registers the class Pair</li> </ol> <p>Now, as you can see, this isn't very flexible, but it does work, and it's a two-way street:</p> <pre><code>id&lt;NSCPPObj&gt; obj = [[NSCPPObj::cls() alloc] initWithInt:15]; [obj doSomething]; NSLog(@"%i", [obj somethingThatReturnsAValue]); NSLog(@"%@", obj); NSCPPObj *objAsCPP = (__bridge NSCPPObj *) obj; objAsCPP-&gt;doSomething(); std::cout &lt;&lt; objAsCPP-&gt;somethingThatReturnsAValue() &lt;&lt; std::endl; </code></pre> <p>You can also create the object by using <code>new NSCPPObj(15)</code>, but remember to delete it! Obviously, this can work in a ARC or non-ARC environment, but ARC requires a few extra bridged casts.</p> <p>So, I come to the real question:<br> What are the pros/cons of this design structure? I can list a few off of the top of my head:</p> <p>Pros:</p> <ol> <li>Operator Overloading with C++</li> <li>Dynamic method binding with ObjC</li> <li>Can be constructed in either a C++ or ObjC fashion</li> </ol> <p>Cons:</p> <ol> <li>Hard-to-read implementation</li> <li>Selectors &amp; bindings must be added for every C++ implementation added to the interface</li> <li>Class object cannot be referenced directly</li> </ol> <p>So, after all that, <em>would you recommend this design structure in an application?</em> and why.</p>
 

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