[swift-users] How to store ref to any kind of function, and call with it argument list?

[Slava Pestov]

Unfortunately we don’t have a way to invoke a function with a runtime argument list because that would require runtime code generation in the most general case.

I would hack around it by handling the common cases of no arguments, 1 argument, 2 arguments, etc up to some fixed number of arguments that you consider “enough”. Use a switch on the type of the function.

Slava

> On Nov 3, 2017, at 2:21 PM, C. Keith Ray via swift-users <swift-users at swift.org> wrote:
> 
> In the code below, I'm trying to store a reference to a function with any number of arguments, with any return type. And I want to be able to invoke it. 
> 
> Help?
> 
> See the comments with "*******"
> 
> typealias Void = ()
> 
> func equalTypes(_ me: [Any.Type], _ other: [Any.Type]) -> Bool {
>     guard me.count == other.count else { return false }
>     
>     for i in 0 ..< me.count {
>         if me[i] != other[i] { return false }
>     }
>     return true
> }
> 
> struct Function {
>     var returnType: Any.Type
>     var argTypes: [Any.Type]
>     var function: Any // ******* any function *******
>     
>     func perform(_ args: [Any]) -> Any {
>         // ******* call function() with args, return result *******
>         return 0
>     }
>     
>     func isCompatible(_ other: Function) -> Bool {
>         return self.returnType == other.returnType &&
>             equalTypes(argTypes, other.argTypes)
>     }
> }
> 
> func vToV() {
>     print("vToV")
> }
> 
> func intToInt(_ i: Int) -> Int {
>     print("intToInt")
>     return 4
> }
> 
> let f = Function(returnType: Void.self,
>                  argTypes: [],
>                  function: vToV)
> let r = f.perform([])
> print(r)
> 
> let f2 = Function(returnType: Int.self,
>                  argTypes: [Int.self],
>                  function: intToInt)
> let r2 = f2.perform([12])
> print(r2)
> 
> assert(f.isCompatible(f))
> assert(!f.isCompatible(f2))
> 
> 
> --
> C. Keith Ray
> Senior Software Engineer / Trainer / Agile Coach
> * http://www.thirdfoundationsw.com/keith_ray_resume_2014_long.pdf <http://www.thirdfoundationsw.com/keith_ray_resume_2014_long.pdf>
> 
> 
> 
> _______________________________________________
> swift-users mailing list
> swift-users at swift.org
> https://lists.swift.org/mailman/listinfo/swift-users

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