Why cannot index priorityqueue.NewWith (value of type func(comparator utils.Comparator) *priorityqueue.Queue)?

[aldalee]

This is a leetcode problem:merge k sorted lists, I want to use a heap to solve it, and the following code can be AC.

package main

import pq "github.com/emirpasic/gods/queues/priorityqueue"

type ListNode struct {
	Val  int
	Next *ListNode
}

func mergeKLists(lists []*ListNode) *ListNode {
	heap := pq.NewWith(func(a, b any) int {
		return a.(*ListNode).Val - b.(*ListNode).Val
	})
	for _, list := range lists {
		if list != nil {
			heap.Enqueue(list)
		}
	}
	if heap.Empty() {
		return nil
	}
	v, _ := heap.Dequeue()
	head := v.(*ListNode)
	cur, pre := head, head
	for !heap.Empty() {
		if cur.Next != nil {
			heap.Enqueue(cur.Next)
		}
		v, _ := heap.Dequeue()
		cur = v.(*ListNode)
		pre.Next = cur
		pre = cur
	}
	return head
}

But type assertion is required, and I want to add generics to solve this problem. I noticed that the following libraries have already introduced generics: https://github.com/emirpasic/gods/blob/master/queues/priorityqueue/priorityqueue.go
So I adjusted my code and added generics:

package main

import "github.com/emirpasic/gods/queues/priorityqueue"

type ListNode struct {
	Val  int
	Next *ListNode
}

func mergeKLists(lists []*ListNode) *ListNode {
	heap := priorityqueue.NewWith[*ListNode](func(a, b *ListNode) int {
		return a.Val - b.Val
	})

	for _, list := range lists {
		if list != nil {
			heap.Enqueue(list)
		}
	}
	if heap.Empty() {
		return nil
	}
	head, _ := heap.Dequeue()
	cur, pre := head, head
	for !heap.Empty() {
		if cur.Next != nil {
			heap.Enqueue(cur.Next)
		}
		cur, _ = heap.Dequeue()
		pre.Next = cur
		pre = cur
	}
	return nil
}

But when I import "github.com/emirpasic/gods/queues/priorityqueue" and build the code on https://go.dev/play, I meet the error:

go: finding module for package github.com/emirpasic/gods/queues/priorityqueue
go: downloading github.com/emirpasic/gods v1.18.1
go: found github.com/emirpasic/gods/queues/priorityqueue in github.com/emirpasic/gods v1.18.1
./prog.go:11:31: invalid operation: cannot index priorityqueue.NewWith (value of type func(comparator utils.Comparator) *priorityqueue.Queue) 

Here are some source codes:

// NewWith instantiates a new empty queue with the custom comparator.
func NewWith[T comparable](comparator utils.Comparator[T]) *Queue[T] {
	return &Queue[T]{heap: binaryheap.NewWith(comparator), Comparator: comparator}
}

// comparable is an interface that is implemented by all comparable types
// (booleans, numbers, strings, pointers, channels, arrays of comparable types,
// structs whose fields are all comparable types).
// The comparable interface may only be used as a type parameter constraint,
// not as the type of a variable.
type comparable interface{ comparable }

But, I have added generics and implemented comparators, why are there still errors?

Meanwhile, while compiling the code locally, I encountered this error again:

D:\space\algorithm\leetcode-top-interview-questions\src> go build .\problem_0023_merge_k_sorted_lists.go
# github.com/emirpasic/gods/queues/priorityqueue
D:\opt\go1.22\gopath\pkg\mod\github.com\emirpasic\[email protected]\queues\priorityqueue\iterator.go:13:7: type instantiation requires go1.18 or later (-lang was set to go1.2; check go.mod)
D:\opt\go1.22\gopath\pkg\mod\github.com\emirpasic\[email protected]\queues\priorityqueue\iterator.go:16:15: type parameter requires go1.18 or later (-lang was set to go1.2; check go.mod)
D:\opt\go1.22\gopath\pkg\mod\github.com\emirpasic\[email protected]\queues\priorityqueue\iterator.go:16:17: predeclared comparable requires go1.18 or later (-lang was set to go1.2; check go.mod)
D:\opt\go1.22\gopath\pkg\mod\github.com\emirpasic\[email protected]\queues\priorityqueue\iterator.go:17:12: type instantiation requires go1.18 or later (-lang was set to go1.2; check go.mod)
D:\opt\go1.22\gopath\pkg\mod\github.com\emirpasic\[email protected]\queues\priorityqueue\priorityqueue.go:32:12: type parameter requires go1.18 or later (-lang was set to go1.2; check go.mod)
D:\opt\go1.22\gopath\pkg\mod\github.com\emirpasic\[email protected]\queues\priorityqueue\priorityqueue.go:32:14: predeclared comparable requires go1.18 or later (-lang was set to go1.2; check go.mod)
D:\opt\go1.22\gopath\pkg\mod\github.com\emirpasic\[email protected]\queues\priorityqueue\priorityqueue.go:33:14: type instantiation requires go1.18 or later (-lang was set to go1.2; check go.mod)
D:\opt\go1.22\gopath\pkg\mod\github.com\emirpasic\[email protected]\queues\priorityqueue\priorityqueue.go:34:13: type instantiation requires go1.18 or later (-lang was set to go1.2; check go.mod)
D:\opt\go1.22\gopath\pkg\mod\github.com\emirpasic\[email protected]\queues\priorityqueue\priorityqueue.go:37:10: type parameter requires go1.18 or later (-lang was set to go1.2; check go.mod)
D:\opt\go1.22\gopath\pkg\mod\github.com\emirpasic\[email protected]\queues\priorityqueue\priorityqueue.go:42:14: type parameter requires go1.18 or later (-lang was set to go1.2; check go.mod)
D:\opt\go1.22\gopath\pkg\mod\github.com\emirpasic\[email protected]\queues\priorityqueue\iterator.go:13:7: too many errors

My Go version is go version go1.22.0 windows/amd64. And this is my go.mod

module leetcode-top-interview-questions
go 1.22
require github.com/emirpasic/gods v1.18.1
require github.com/emirpasic/gods/v2 v2.0.0-alpha // indirect

How can I solve the above two problems? Thank you!

[PapaCharlie]

Hey @aldalee, now that you're using the new major version with generics, you need to import it like this:

import "github.com/emirpasic/gods/v2/queues/priorityqueue"

In all your error messages you're still pulling in v1.18.1