I am trying to type assert from a []Node
, to []Symbol
. In my code, Symbol
implements the Node
interface.
Here is some surrounding code:
43 func applyLambda(args []Node, env Env) Node {
44 if len(args) > 2 {
45 panic("invalid argument count")
46 }
47 fixed, rest := parseFormals(args.([]Symbol))
48 return Func{
49 Body: args[1],
50 FixedVarNames: fixed,
51 RestVarName: rest,
52 }
53 }
Here's the error I get:
./builtins.go:47: invalid type assertion: args.([]Symbol) (non-interface type []Node on left)
I'm sure there's a good reason for this. What's the best way to proceed?
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)