IOS SWIFT: Declaration is only valid at file scope

Question

Normally in C# I used to implement extension methods in a separate class (named 'ExtensionMethods') and used in the project.

Here in my first swift iphone App I need to implement some extension methods to 'String' class but providing me with this error

This works perfect with swift Playground but not sure how to use in a real project. really appreciate if someone can guide me with this. Thanks.

Answer 1

The extension must be at the root level - don't embed them into a class or whatever. So just write:

import UIKit

extension String {
    var doubleValue: Double {
        ...
    }
}

extension String {
    func doubleValueT() -> Double {
        ...
    }
}

Note that you can also combine them into a single extension:

import UIKit

extension String {
    var doubleValue: Double {
        ...
    }

    func doubleValueT() -> Double {
        ...
    }
}