[swift-users] Strange Behavior With Closures

bwm003 at gmail.com bwm003 at gmail.com
Wed May 4 20:19:51 CDT 2016

Hi Everyone,
I was playing around in Xcode 7.3 with this code...


* *  Represents a future value of type U, from a computation that has not
been done yet.*

* */*

*public struct Promise<T, U> {*

*    var futureValue: T -> U*

*    public func then<T,U,V>(closure: U -> V) -> Promise<T, V> {*

*        return Promise<T, V>(futureValue: {*

*            input in*

*            let value = futureValue(input)*

*            return closure(value)*

*        })*

*    }*


and came across the following error:

*error: cannot invoke value of type 'T -> U' with argument list '((T))'*

Can someone explain what is going on here? It looks like my closure should
be accepting a value of T, but for some reason the types aren't matching up.
Thanks, Blake
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