Generic iterator in Go

iterator.go

package main

import (
	"fmt"
	"strings"
)

// Generic iterator function type
type iteratorFunc[T any] func() *T;

// Generic function for iteration
func next[T any](iterator iteratorFunc[T]) *T { return iterator() }

// Generic function executing a given function for each item in iterator
func forEach[T any](iterator iteratorFunc[T], body func(T)) {
	for ptr := next(iterator); ptr != nil; ptr = next(iterator) {
		body(*ptr)
	}
}

// Generic predicate
type predicate[T any] func(item T) bool;

// Generic function filtering based on a given predicate
func filter[T any](iterator iteratorFunc[T], predicate func(T) bool) iteratorFunc[T] {
	return func() *T {
		var item *T
		for item = next(iterator); item != nil && !predicate(*item); item = next(iterator) { }
		return item
	}
}

// Generic function that generates an iterator from a given slice
func iteratorFromSlice[T any](items []T) iteratorFunc[T] {
	return func() *T {
		if len(items) < 1 {
			return nil
		}
		
		firstItem := &items[0]
		items = items[1:]
		return firstItem
	}
}

type user struct {
	name string
	age  int
}

func main() {
	users := []user{
		user{name: "Foo", age: 42}, 
		user{name: "Bar", age: 43}, 
		user{name: "FooBar", age: 44}, 
	}
	forEach(
		filter(
			iteratorFromSlice(users),
			func(u user) bool { return strings.HasPrefix(u.name, "Foo"); }),
		func(u user) { fmt.Printf("User is %s\n", u.name) })
}