My String[] really is substitutable for an interface{}[] within the context of a function that doesn't modify it, but there seems no way to express this. Not r

My String[] really is substitutable for an interface{}[] within the context of a function that doesn't modify it, but there seems no way to express this. Not really. The underlying representation is different, an interface is a pointer to a type and a pointer to a value. A string is a pointer to the character data and a length. It'd get even more difficult with other data types, since an interface is two machine words, and other data types can be anything. Since a slice is backed by an array, there would be no way to do reliable indexing. I do see your point: a slice could hold the type of its elements and then you'd have to prove that no other types are stored in the slice. But that's not really simple either. A more consistent solution would be to store 'interface values' as pointers (rather than a pair of pointers). Then you could use a slice of pointers as a slice of interface{} (or any other interface the pointed-to type supports).