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copied!<p>@Ahruman's answer is correct, if you're dealing with objects. Let me suggest some alternatives:</p> <ol> <li><code>valueForKey:</code>: If you use <code>[myObject valueForKey:@"myPropertyName"]</code>, it will return an object. If the property corresponds to some sort of primitive (<code>int</code>, <code>float</code>, <code>CGRect</code>, etc), then it will be boxed for you into an <code>NSNumber</code> or <code>NSValue</code> (as appropriate). If it comes back as an <code>NSNumber</code>, you can then easily extract a double representation (<code>doubleValue</code>) and use that as an <code>NSTimeInterval</code> to create an <code>NSDate</code>. I would probably recommend this approach.</li> <li><p>Special case each type. <code>property_getAttributes()</code> returns a <code>char*</code> representing all of the attributes of the property, and you can extract the type by doing this:</p> <pre>const char * type = property_getAttributes(class_getProperty([self class], "myPropertyName")); NSString * typeString = [NSString stringWithUTF8String:type]; NSArray * attributes = [typeString componentsSeparatedByString:@","]; NSString * typeAttribute = [attributes objectAtIndex:0]; NSString * propertyType = [typeAttribute substringFromIndex:1]; const char * rawPropertyType = [propertyType UTF8String]; if (strcmp(rawPropertyType, @encode(float)) == 0) { //it's a float } else if (strcmp(rawPropertyType, @encode(int)) == 0) { //it's an int } else if (strcmp(rawPropertyType, @encode(id)) == 0) { //it's some sort of object } else ....</pre> <p>This is pedantically more correct than Louis's answer, because while <em>most</em> types have a single-character encoding, <em>they don't have to</em>. (his suggestion assumes a single-character encoding)</p></li> <li><p>Finally, if you're doing this on a subclass of <code>NSManagedObject</code>, then I would encourage checking out <code>NSPropertyDescription</code>.</p></li> </ol> <p>From these alternatives, you can probably see that letting the runtime box the value for you is probably simplest.</p> <p><strong>edit</strong> extracting the type:</p> <p>From the code above, you can extract the class name like so:</p> <pre><code>if ([typeAttribute hasPrefix:@"T@"] && [typeAttribute length] > 1) { NSString * typeClassName = [typeAttribute substringWithRange:NSMakeRange(3, [typeAttribute length]-4)]; //turns @"NSDate" into NSDate Class typeClass = NSClassFromString(typeClassName); if (typeClass != nil) { [object setValue:[self convertValue:self.value toType:typeClass] forKey:element]; } } </code></pre> <p>And then instead of using class method categories to do the conversion (ie, <code>[NSDate convertToDate:]</code>), make a method on <code>self</code> that does that for you and accepts the desired type as a parameter. You could (for now) do it like:</p> <pre><code>- (id) convertValue:(id)value toType:(Class)type { if (type == [NSDate class]) { return [NSDate convertToDate:value]; } else if (type == [NSString class]) { return [NSString convertToString:value]; } ... } </code></pre> <p>Part of me is wondering, though: why on earth are you needing to do things this way? What are you making?</p>

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