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POIs it possible to have a __block variable point to different objects, without altering the blocks copied before?
 

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  1. POIs it possible to have a __block variable point to different objects, without altering the blocks copied before?
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    <p>I've asked a similar question before, but this time the situation is a bit different.</p> <p>For one, this time around I'm using ARC (inviting a whole new world of problems). Second: The code I have basically works, but I'm wondering if I could do with less code.</p> <p>Right now, my code looks like this:</p> <pre><code>__weak CustomType *Object; void (^doAverage)(CustomType *, int, int) = ^(CustomType *Trigger, int Val1, int Val2) { //Calculations with Trigger } CustomType *(^Add)(int, CustomType *) = ^(int Val1, CustomType *NewObject) { //Checks prerequisites, and returns either the passed object after adding it to //an array or nil, if the prerequisites haven't been met. } </code></pre> <p>Now, further down the line, I'm doing this:</p> <pre><code>Object = Add(-1, [CustomType makeObjectWithParameters]); [Object addCallback:^{ doAverage(Object, 56, 57); }]; </code></pre> <p>Inside <code>addCallback</code>, the passed block with the call to <code>doAverage</code> is sent a <code>copy</code> message and saved for later execution.</p> <p>This works, no retain cycles, the callbacks fold if the object is deallocated.</p> <p>But it's not 'as elegant' as I'd like.</p> <p>What I'd like would be something along these lines:</p> <pre><code>__block __weak CustomType *Object; CustomType *(^Add)(int, CustomType *) = ^(int Val1, CustomType *NewObject) { //Checks prerequisites, and returns either the passed object after adding it to //an array or nil, if the prerequisites haven't been met. Object = NewObject; } </code></pre> <p>And further down the line:</p> <pre><code>[Add(-1, [CustomType makeObjectWithParameters]) addCallback:^{ doAverage(Object, 56, 57); }]; </code></pre> <p>However if I do it like this, it'll change the <code>Object</code> passed to the callback to whatever <code>Add</code> I called last, which isn't what I want.</p> <p>Basically I'd need to <code>set</code> the value of <code>Object</code> in a block and then <code>copy</code> that reference as a parameter, instead of passing the reference to the variable itself.</p> <p>Furthermore, as a second step, it'd be about perfect, if I didn't have to pass the parameter <code>Object</code> in the first place, but could use it in the block. But if I do that, the variable in the block will default to nil when the block is finally called (well past the expiration of the scope it was defined in).</p> <p>So instead of:</p> <pre><code>void (^doAverage)(CustomType *, int, int) = ^(CustomType *Trigger, int Val1, int Val2) { //Calculations with Trigger } </code></pre> <p>I'd like to do use:</p> <pre><code>void (^doAverage)(int, int) = ^(int Val1, int Val2) { //Calculations with Object } </code></pre> <p>With whatever value <code>Object</code> (weak reference) had at that moment in time.</p> <p>Is either of the two somehow possible?</p> <p>Thank you very much.</p> <p>Edit:</p> <p>Following the below suggestion, I refactored my code like this:</p> <pre><code>typedef BOOL (^stackBlock_t)(); typedef BOOL (^CallBlock_t)(__weak id Object); -(void) addCallback(CallBlock_t)B { stackBlock_t stackBlock = ^{ __weak id Object = self; return B(Object); }; Callback = [stackBlock copy]; } </code></pre> <p>I'm trying to call this construct with:</p> <pre><code>[Add(-1, CustomType makeObjectWithParameters]) addCallBack:^{ doAverage(Object, 56, 57); }]; </code></pre> <p>However <code>Object</code> isn't defined for the <code>doAverage</code> block for some reason, and I don't quite know why. After all, it's a block of type <code>CallBlock_t</code>, which takes a parameter of type <code>id</code> and the name <code>Object</code>. Shouldn't it 'know' about the variable <code>Object</code> then?</p> <p>Edit 2: After a bit of tinkering around (namely using the actual type and stuff), it now gives me a different error message: <code>Incompatible block pointer types sending 'void (^)(void)' to parameter of type 'CallBlock_t'</code>, though I'm not. I want that block to return a <code>BOOL</code> and take the argument <code>Object</code>...what am I doing wrong?</p> <p>Edit 3: I may have found it. I was missing something in my <code>addCallback</code> call. I have yet to test it, but it would seem, that I'm required to call it like this:</p> <pre><code>[Add(-1, CustomType makeObjectWithParameters]) addCallBack:^(CustomObject *Object){ doAverage(Object, 56, 57); }]; </code></pre> <p>Thinking about it, it makes sense...it's horrible on the eyes, but it makes sense. And it works like a charm. I don't even need excess variables of type <code>__block</code> any more.</p>
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    1. COso what have you tried? does it not work?
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    2. CO@newacct I've already posted what I tried. I tried it with __weak __block, which lead to every instance of Add using the very same variable instead of a copy of the current state. For clarification purposes, I'm using a block to invoke a block with specific parameters. However one of these parameters...namely `Object`, does not behave like I'd like it to.
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