OrderedMap is a Go implentation of Python's OrderedDict class, a map that preserves the order of insertion, so key:value pairs can be iterated in the order they where added. It can also be used as a stack (LIFO) or queue (FIFO).
Install the package from command line with the following command
go get -u github.com/secnot/orderedmapAnd then import in your source file
import "github.com/secnot/orderedmap"Basic operations
package main
import (
"github.com/secnot/orderedmap"
"fmt"
)
func main() {
// Create
om := orderedmap.NewOrderedMap()
// Insert
om.Set("John Smith", 44)
om.Set("Laura Paro", 39)
om.Set("Alison Rogers", 52)
// Update
om.Set("Alison Rogers", 51)
// Get
if age, ok := om.Get("John Smith"); ok {
fmt.Printf("John Smith age: %v", age)
}
// Get the last key added
if name, age, ok := om.GetLast() {
fmt.Printf("%v age: %v\n", name, age)
}
// Delete
om.Delete("John Smith")
}Pop the last key from the map
key, value, ok := om.PopLast()
// > Alison Rogers, 52, trueIterate over the Map elements in insertion order
package main
import (
"github.com/secnot/orderedmap"
"fmt"
)
func main() {
om := orderedmap.NewOrderedMap()
om.Set("John Smith", 44)
om.Set("Laura Paro", 39)
om.Set("Alison Rogers", 52)
// Iterate
iter := om.Iter()
for key, value, ok := iter.Next(); ok; key, value, ok = iter.Next() {
fmt.Printf("%v: %v", key, value)
}
// > John Smith: 44
// > Laura Paro: 39
// > Alison Rogers: 52
}While iterating over an OrderedMap only three methods can be called safely, Get, Set, and Delete, with some limitations/gotchas for the last two.
Set can update the value of any existing key without problems, but new keys are inserted at the end of the Map so they will be also iterated over, this can cause bugs on innocent-looking code:
package main
import (
"github.com/secnot/orderedmap"
"fmt"
)
func main() {
om := orderedmap.NewOrderedMap()
om.Set("John Smith", 44)
om.Set("Laura Paro", 39)
// This is an infinite loop
iter := om.Iter()
for name, age, ok := iter.Next(); ok; name, age, ok = iter.Next() {
om.Set("Dr. " + name, age)
fmt.Printf("%v\n", name)
}
// Prints
// > John Smith
// > Laura Paro
// > Dr. John Smith
// > Dr. Laura Paro
// > Dr. Dr. John Smith
// > Dr. Dr. Laura Paro
// .....
// Iterating in reverse order avoids this problem
iter = om.IterReverse()
for name, age, ok := iter.Next(); ok; name, age, ok = iter.Next() {
om.Set("Dr. " + name, age)
}
}Delete is more restrictive and can only be used to delete the key being iterated over at that moment.
package main
import "github.com/secnot/orderedmap"
func main() {
om := orderedmap.NewOrderedMap()
om.Set("first", 1)
om.Set("second", 2)
om.Set("third", 3)
// This is safe
iter := om.Iter()
for k, _, ok := iter.Next(); ok; k, _, ok = iter.Next() {
om.Delete(k)
}
// This is NOT
iter = om.Iter()
for _, _, ok := iter.Next(); ok; _, _, ok = iter.Next() {
om.Delete("another key")
}
} Lastly an OrderedMap can also be handled as a queue or a stack with:
- GetLast | GetFirst : key:value for both ends of the queue or stack, without modifying the map
- PopLast: Pop the value at the top of the Stack.
- PopFirst: Pop next queue element
- MoveLast | MoveFirst: Move elements to either end of the queue or stack
type OrderedMap struct {
// contains filtered or unexported fields
}func NewOrderedMap() *OrderedMapCreate an empty OrderedMap
func (*OrderedMap) Delete(key interface{})Delete a key:value pair from the map.
func (om *OrderedMap) Get(key interface{}) (value interface{}, ok bool)Get the value of an existing key, leaving the map unchanged
func (om *OrderedMap) GetFirst() (key interface{}, value interface{}, ok bool)Get the key value for the beginning element, leaving the map unchanged
func (om *OrderedMap) GetLast() (key interface{}, value interface{}, ok bool)Get the key and value for the last element added, leaving the map unchanged
func (om *OrderedMap) Iter() *MapIteratorCreate a map iterator
func (om *OrderedMap) IterReverse() *MapIteratorCreate a reverse order map iterator
func (om *OrderedMap) Len() intReturn the number of elements in an OrderedMap
func (om *OrderedMap) Move(key interface{}, last bool) (ok bool)Move an existing key to either the end of the OrderedMap
func (om *OrderedMap) MoveFirst(key interface{}) (ok bool)Shortcut to Move a key to the beginning of the map
func (om *OrderedMap) MoveLast(key interface{}) (ok bool)Shortcut to Move a key to the end of the map
func (om *OrderedMap) Pop(last bool) (key interface{}, value interface{}, ok bool)Pop and return key:value for the newest or oldest element on the OrderedMap.
func (om *OrderedMap) PopFirst() (key interface{}, value interface{}, ok bool)Shortcut to Pop the first element
func (om *OrderedMap) PopLast() (key interface{}, value interface{}, ok bool)Shortcut to Pop the last element
func (om *OrderedMap) Set(key interface{}, value interface{})Sets the key value, if the key exists it overwrites the existing entry, and the original insertion position is left unchanged, otherwise the key is inserted at the end.
func (om *OrderedMap) String() stringStringer interface
type MapIterator struct {
// contains filtered or unexported fields
}func (mi *MapIterator) Next() (key interface{}, value interface{}, ok bool)Return iterators next key:value pair until the map is exhausted