An *OrderedMap is a high performance ordered map that maintains amortized O(1) for Set, Get, Delete and Len:

import "github.com/elliotchance/orderedmap/v3"

func main() {
	m := orderedmap.NewOrderedMap[string, any]()

	m.Set("foo", "bar")
	m.Set("qux", 1.23)
	m.Set("123", true)

	m.Delete("qux")
}

Internally an *OrderedMap uses the composite type map combined with a trimmed down linked list to maintain the order.

The following methods all return iterators that can be used to loop over elements in an ordered map:

• AllFromFront()
• AllFromBack()
• Keys()
• Values()

// Iterate through all elements from oldest to newest:
for key, value := range m.AllFromFront() {
	fmt.Println(key, value)
}

Iterators are safe to use bidirectionally, and will return nil once it goes beyond the first or last item. If the map is changing while the iteration is in-flight it may produce unexpected behavior.

If you want to get a slice of the map keys or values, you can use the standard slices.Collect method with the iterator returned from Keys() or Values():

fmt.Println(slices.Collect(m.Keys())
// [A B C]

Likewise, calling maps.Collect on the iterator returned from AllFromFront() will create a regular unordered map from the ordered one:

fmt.Println(maps.Collect(m.AllFromFront())
// [A:1 B:2 C:3]

If you don't want to use iterators, you can also manually loop over the elements using Front() or Back() with Next():

// Iterate through all elements from oldest to newest:
for el := m.Front(); el != nil; el = el.Next() {
    fmt.Println(el.Key, el.Value)
}

// You can also use Back and Prev to iterate in reverse:
for el := m.Back(); el != nil; el = el.Prev() {
    fmt.Println(el.Key, el.Value)
}