Can I type assert a slice of interface values?

Question

I am trying to type assert from a []Node, to []Symbol. In my code, Symbol implements the Node interface.

Here is

Answer 1

In saying x.(T) variable x should be of interface type, because only for variables of type interface dynamic type is not fixed. And while Node is an interface, []Node is not. A slice is a distinct, non-interface type. So it just doesn't make sense to assume a slice of interface values is an interface too.

Type Node has a clear definition in your code and thus is an interface. You have specified the list of methods for it. Type []Node isn't like that. What methods does it define?

I understand where your are coming from with this. It may be a useful shortcut, but just doesn't make sense. It's kind of like expecting syms.Method() to work when syms's type is []Symbol and Method is for Symbol.

Replacing line 47 with this code does what you want:

symbols := make([]Symbol, len(args))
for i, arg := range args { symbols[i] = arg.(Symbol) }
fixed, rest := parseFormals(symbols)

Answer 2

Go does not allow this. You need to convert Node to Symbol individually.

The reason why it isn't allowed is that []Node and []Symbol have different representations, so the conversion would need to allocate memory for []Symbol.