What's the purpose of unsigned type here?

Sorry for the multitude of开发者_JAVA百科 iPhone Programming newb questions but..

what is the reason for having an unsigned type for something such as

- (unsigned)count

for the NSArray class.

Why not just define it as

- (int)count

?

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An array can't have a negative number of items, so an unsigned integer is a much better match for the kinds of values this method will actually return.