The type declaration is the final arbiter. Since it says "any type", it means exactly that: you are claiming your function is prepared to handle *any type* the caller wishes to specify. It is not "soft", nor "variable" in the sense you intend: it is a hard requirement that your function must be prepared to handle whatever type the caller wants there.

But instead your function requires that it be String, because both sides of (==) must be the same type. This violates the type signature'a assertion that the caller can specify any type.