CODEWITHSUNDEEP
swift
Blazej SLEBODA
Blazej SLEBODA

Reputation: 9925

How to access an anonymous parameter within a method?

How can I access the str label inside the function body? If it's impossible then why the compiler doesn't throw an error ?

class Test {
    func methodA(str _: String) {
    }

    func methodB() {
        methodA(str: "")
    }
}

Upvotes: 0

Views: 349

Answers (1)

rmaddy
rmaddy

Reputation: 318854

Using _ for the parameter name means you have no need to use the parameter within the method. The str argument label has no use inside the implementation of the method itself. It's only useful in the calling syntax.

If you actually have a need to use a parameter in a method, don't give it the anonymous name of _. Give it a useful name so it can be referenced in the implementation of the method. Or simply remove the _ so both the parameter name and label are the same.

Either do:

func methodA(str: String) {
    // do something with str
}

or something like:

func methodA(str val: String) {
    // do something with val
}

In both cases the caller is the same as you currently have:

methodA(str: "")

The only time you would want an anonymous parameter name is if your implementation of the method doesn't actually make use of the parameter. Maybe the implementation isn't finished or over time it's changed and a parameter isn't needed any more and you don't want to update lots of existing code calling the method.

There is a compiler setting to get warnings about unused parameters. If you have an unused parameter, changing the name to _ eliminates the warning.

See Function Argument Labels and Parameter Names in the Swift book (though it doesn't cover this case of anonymous parameter names).

Upvotes: 1

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