Default value of T any

Getting Help
1

I have the following code which is an exercise from here (A Tour of Go).

package main

import (
	"errors"
	"fmt"
)

// List represents a singly-linked list that holds
// values of any type.
type List[T any] struct {
	next *List[T]
	val  T
}

func (head List[T]) my_next() (T, error) {
    if head.next == nil {
        // QUESTION ABOUT THIS LINE
        return head.val, errors.New("no next element")
    }
    return head.next.val, nil;
}

func main() {
    l := List[int]{nil, 123};
    fmt.Println(l.my_next());

}

The my_next method is supposed to get the next element in the linked list. If we are at the tail, it should return a non-nil error.

If head.next == nil, then we really shouldn’t returning anything for the value (we should only return an error). I tried return nil, errors.New("no next element") but that would not compile. In short, this case worked out because I can just return head.val as a dummy/placeholder value which I know is of type T.

Is there any way I can construct a default of/for type T any?
Maybe I’m looking for a “constructable” or “defaultable” interface or something similar?

Very new to go, any and all help is appreciated!

2

You could do something like this:

if head.next == nil {
	var empty T
	return empty, errors.New("no next element")
}
1 Like
3

I figured I was missing something simple like that. Thanks so much for your help! :grinning: