Swift：swift 访问 function 在结构无 init

Question

I'm trying to access to function in struct like this

struct DoSomething {
    var str: String

    func processNumber(number: Int) -> String {
        return "\(number)"
    }
}

let number = DoSomething().processNumber(number: 10)
print(number)

But I'm getting this error:

Missing argument for parameter 'str' in call

Any of you knows how can Access the function in the struct.

I'll really appreciate your help.

Answer 1

You should pass a paramter like this be

let number = DoSomething(str:"someValue").processNumber(number: 10)

As there is no () init in that case, if you need it a separate logic do

class func processNumber(number: Int) -> String {
    return "\(number)"
}

and call like

let number = DoSomething.processNumber(number: 10)

note if the var var str: String has no usage you should not create it either

Answer 2

You have to initialize str when creating an instance of DoSomething .

Either assign a default value in the struct

struct DoSomething {

    var str: String = ""

    ....

}

let number = DoSomething().processNumber(number: 10)

Or in the initializer which has the signature init(str: String)

let number = DoSomething(str: "").processNumber(number: 10)

Answer 3

The issue can be resolved by declaring the str as an optional.

struct DoSomething {
    var str: String?

    func processNumber(number: Int) -> String {
        return "\(number)"
    }
}

let number = DoSomething().processNumber(number: 10)
print(number)