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A method in a class is defined as func yo(hithere v: Int) -> String { return "hi " + String(v) } Note the -> String after the variable declaration defines the return type. And you're prefixing the variable in the argument list with some random text.

You then call yourclassintance.yo(hithere: 3). You'd normally change hithere with with or by to fit into with Swift convention, though. You can also define static methods if you prefix them with class, and within such a method self refers to the type of the class.