On 09/03/2017 11:05, Rien via swift-users wrote:
I am trying to achieve the following:
enum FunctionResult<T> {
case success(T)
case error(String)
}
func tester<T>(test: (…) -> FunctionResult<T>, onError: (String) -> T) -> T {
…
}
The problem is of course the (…) that simply does not work.
I would like to use this generic with a variety of different signatures, i.e.:
let result1 = tester(test: myfunc1(param: 26) -> FunctionResult<Bool>, onError:
{ … handle the error ... })
let result2 = tester(test: myfunc2(param: “A String") -> FunctionResult<Bool>,
onError: { … handle the error ... })
let result3 = tester(test: myfunc3(param: 26, param2: “String") ->
FunctionResult<Int>, onError: { … handle the error ... })
Is this at all possible?
This should do it:
func tester<T>(test: @autoclosure () -> FunctionResult<T>,
onError: (String) -> T) -> T {
switch test() {
case .success(let value): return value
case .error(let error): return onError(error)
}
}
The insight is that you don't really want to pass a function in the
first parameter, but only the _result_ of that function call. The
@autoclosure attribute then makes sure that the expression you pass to
tester is only evaluated inside tester. You can leave it out if you want
(if you do, replace `switch test()` with `switch test`).
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