How to make a custom function with + operator in Swift

Question

I'm looking at this code from rosettacode.org and one of the functions defined within it is this:

class MyClass {
    static func + <T>(el: T, arr: [T]) -> [T] {
        var ret = arr
    
        ret.insert(el, at: 0)
    
        return ret
    }
}

The compiler has this to say about it:

Member operator '+' must have at least one argument of type 'MyClass'

I updated the method to make it it static, as follows:

static func + <T: Sequence>(el: T, arr: [T]) -> [T] {
    var ret = arr
    
    ret.insert(el, at: 0)
    
    return ret
}

That doesn't get rid of the compiler error. I tried Googling it, but I'm not coming up with any short, simple answers. Any ideas how I might quell this error?

Answer 1

As explained by @MartinR in the comments, you need to put this function at the top level (NOT inside a class).

import Foundation

// Will compile fine from here as is
func + <T>(el: T, arr: [T]) -> [T] {
    var ret = arr
    ret.insert(el, at: 0)
    return ret
}

class TableGenerator {
    // will require at least one argument of the function to be of `TableGenerator` type
}