具有泛型参数类型的Swift函数

Question

I'm looking for an easy and convenient way to implement a function that accepts all types that can be casted to strings eg: myFunc("This string") or myFunc(2) or myFunc(true) . I thought this must be possible with generic parameters and tried something like this:

func myFunc<T: StringLiteralConvertible>(param: T? = nil) -> String {
   // ...
   return "\(param)"
}

but I had no success so far.

Answer 1

Use CustomStringConvertible , not StringLiteralConvertible :

func myFunc<T: CustomStringConvertible>(param: T? = nil) -> String {
    // ...
    return "\(param)"
}

myFunc("Grimxn") // Optional("Grimxn")
myFunc(12) // Optional(12)
myFunc(true) // Optional(true)
myFunc(-1.234) // Optional(-1.234)
//myFunc() // doesn't work. Compiler can't infer T

These will give Optionals because you are casting them to T? to allow your nil default. Drop the default (it doesn't work anyway - nil can't imply T ) to get rid of the Optional .

func myFunc<T: CustomStringConvertible>(param: T) -> String {
    // ...
    return "\(param)"
}

myFunc("Grimxn") // "Grimxn"
myFunc(12) // "12"
myFunc(true) // "true"
myFunc(-1.234) // "-1.234"
//myFunc((1,2)) // doesn't compile
myFunc(NSDate()) // "2015-10-26 10:44:49 +0000"