custom compare method in objective c

I'm trying to use a custom compare method (for use with sortedArrayUsingSelector:) and on another website I got that the format is:

-(NSComparisonResult) orderByName:(id)otherobject {

That's all very well and good, except how do I compare the otherObject to anything as there's only one thing passed to the method?

Like how does the NSString开发者_运维知识库 method of compare: compare 2 strings when only one string is passed?

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The comparison is always between otherObject and self.