Golang cannot use generic type without instantiation

Issue

I’m trying to define a generic data structure using generics, particularly a rudimentary HashTable, I try the following:

type hashable interface {
    Hash()
}

type Node[K hashable] struct {
    Key   K
    Value any
}

type HashTable[K hashable] struct {
    size  int
    table [][]Node
}

But I get the following error on the line table [][]Node

cannot use generic type Node[K hashable] without instantiation

I’m not instantiating anything, just defining, what does it want me to do?

Solution

Node is a parameterized type, so when you want to use it, you have to instantiate its type parameters.

The type you use to instantiate it can of course be a type parameter of the enclosing type, so simply do it like this:

type HashTable[K hashable] struct {
    size  int
    table [][]Node[K]
}

Answered By – icza

Answer Checked By – Jay B. (GoLangFix Admin)