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POConverting NSArray to NSSet, custom class instances transfer inconsistently
 

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  1. POConverting NSArray to NSSet, custom class instances transfer inconsistently
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    <p>Ran into a interesting little problem. I was writing a method to filter an array to the unique objects:</p> <pre><code>- (NSArray*)distinctObjectsByAddress { NSSet* uniqueSet = [NSSet setWithArray:self]; NSArray* retArray = [uniqueSet allObjects]; return retArray; } </code></pre> <p>and wrote a unit test to check:</p> <pre><code>- (void)testDistinctObjectsByAddress5 { Person* adam1 = [[Person alloc] initWithFirstName:@"adam" lastName:@"adam" andParent:nil]; Person* adam2 = [[Person alloc] initWithFirstName:@"adam" lastName:@"adam" andParent:nil]; testPersonArray = [NSArray arrayWithObjects:adam1,adam2, nil]; NSArray* checkArray = [testPersonArray distinctObjectsByAddress]; STAssertEquals([checkArray count], [testPersonArray count], @"Array %@ counts should match %@ %@",checkArray,adam1,adam2); } </code></pre> <p>Pretty simple. The interesting part is that about 80-90% of the time the test passes and every so often it fails because the <code>distinctObjectsByAddress</code> method only returns one object. I've been able to trace it to the <code>[NSSet setWithArray:self]</code> call but I've also been able to verify that the two person objects are two different objects (at least they have different address). I'm assuming that <code>setWithArray:</code> is just doing a basic address compare but I don't understand why it is sometimes producing two objects like it should and sometimes producing only one.</p> <p>Something I just tried was changing <code>adam2</code> so that the first and last name were not exactly the same as <code>adam1</code>. This seems to fix the error. Does this point to some sort of compiler optimization when the objects are logically the same?</p>
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    1. USJosh Caswell
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    1. COI would guess that the problem is with Person and how it implements the hash and equality methods that NSSet uses.
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    2. COIt'll be using `isEqual:` as defined by the `NSObject` protocol to compare objects; have you implemented it or `hash` on `Person`?
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    3. COIn addition to the hash problem, you're not explicitly testing adam1 and adam2 for nil. If one occasionally fails to init, that would explain the test failure.
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      1. USbneely
 

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