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Strictly speaking, [string UTF8String] is equivalent to '((const char <star>(<star>)(id, SEL))objc_msgSend)(string, selector)'. Since objc_msgSend is vararg function, it will promote it's arguments, so for example method taking float will be called with double. Casting to a proper function type works around that.

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Oh good point, I hadn't considered vararg promotion!

Do you know if casting to a function also make objc_msgSend_stret and objc_msgSend_fpret unnecessary? I haven't yet worked with any methods that return structs or floating point values, so I haven't had to deal with them yet.

Edit: Oh, nope, my bad, objc_msgSend_stret is the one where you definitely have to cast: http://blog.lazerwalker.com/blog/2013/10/12/the-objective-c-...

As you discovered, _stret/_fpret remain necessary.

objc_msgSend()'s type is not expressible in C; the only time it is correct to call objc_msgSend without a cast is when calling a method IMP with the literal vararg type of id (*method) (id self, SEL sel, ...);

In other words, essentially never.

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