In the following code I have a token type that contains a literal value. By using an empty interface I can create a slice of tokens and append tokens that have different types. I don't think it's possible to accomplish the same using generics since we wouldn't be able to infer a type for the Slice of tokens. Is this assumption correct?
type Token struct {
TokenType string
Literal interface{}
}
func main(){
tok1 := &Token{TokenType: "string", Literal: "foo"}
tok2 := &Token{TokenType: "integer", Literal: 10}
tokS := []*Token{tok1, tok2}
}
No.
Given a parametrized Token type as:
type Token[T any] struct {
TokenType string
Literal T
}
each instantiation with a different type argument produces a different (named) type.
In other words, Token[string] is not assignable to Token[int]. Nor is it assignable to Token[any] as any here is used as a static type to instantiate T.
So when you construct a slice with a specific instance of Token[T any], different instances are simply not assignable to its element type:
tokS := []*Token[string]{tok1, tok2}
// invalid: cannot use tok2 (variable of type *Token[int]) as type *Token[string] in array or slice literal
The only slice that can hold different types, as Token[string] and Token[int] is []interface{} or []any.
since we wouldn't be able to infer a type for the Slice of tokens. Is this assumption correct?
Almost. More precisely, the slice of Token wouldn't infer anything because you yourself must construct it with a concrete instantiation of the generic type
Type inference is used to deduce missing type parameters from those already supplied for function arguments. Generic types must be explicitly instantiated, with a concrete type argument for each type parameter.