Dfyjkt

var closureA: (String)->()

class Test 
 func instanceMethod(string: String) 
 


let a = Test()

closureA = Test.instanceMethod(a)

closureA("hello")

Xcode10 Playground show error:

error: cannot assign value of type '(String) -> ()' to type '(String) -> ()'
closureA = Test.instanceMethod(a)

I already read: https://oleb.net/blog/2014/07/swift-instance-methods-curried-functions/

I think you are missing the point of closure, you can't store the function in the closure, but you can store the piece of code that call to the function with the variable you are passing into the closure, and the function still need a class instance to call it, so it should be like this:

var closureA: ((String)->())?

class Test 
 func instanceMethod(string: String) 
 print(string)
 


let a = Test()

//Assume you have a variable `str: String` before hand that will execute the code inside closure
closureA = str in
 a.instanceMethod(string: str)


//Actual call to the closure to execute it
closureA?("hello")

I think is the bug of the playground. If we create a temp closure B, and assign it to closure A. Then it works.

var closureA: (String)->()

class Test 
 func instanceMethod(string: String) 
 print("Test")
 


let a = Test()

let closureB = Test.instanceMethod(a)

closureA = closureB

closureA("hello") // works