Ways to replace massive if statement with alternative construct in Objective-C

Question

I have a fairly lengthy if statement. The if statement examines a string \"type\" to determine what type of object should be instantiated. Here\'s a sample...

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Answer 1

You can use an NSDictionary filled with ObjC 'Blocks' to do a switch-like statement which executes the desired code. So make a dictionary with your string keys mapped to a block of code to execute when each is found:

NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:
                      ^{ NSLog(@"found key1"); }, @"key1", 
                      ^{ NSLog(@"found key2"); }, @"key2", 
                      nil];

You'll probably prepare this dictionary only once at some early stage like in a constructor or a static initializer so that it is ready when your later code executes.

Then instead of your if/else block, slice out the string key from whatever intput you are receiving (or maybe you won't need to slice it, whatever):

NSString *input = ...
NSRange range = ...
NSString *key = [input substringWithRange:range]; 

And do the (fast) dictionary lookup for the code to execute. Then execute:

void (^myBlock)(void) = [dict objectForKey:key];
myBlock();