Basic functions

Basic functions include Set, Get, Delete, Len and Keys.

.gitignore

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+/.idea

README.md

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+# 🔃 github.com/elliotchance/orderedmap [![GoDoc](https://godoc.org/github.com/elliotchance/orderedmap?status.svg)](https://godoc.org/github.com/elliotchance/orderedmap)
+
+The `orderedmap` package provides a high performance ordered map in Go:
+
+```go
+m := orderedmap.NewOrderedMap()
+
+m.Set("foo", "bar")
+m.Set("qux", 1.23)
+m.Set(123, true)
+
+m.Delete("qux")
+
+for _, key := range m.Keys() {
+	value, _:= m.Get(key)
+	fmt.Println(key, value)
+}
+```
+
+Internally an `*OrderedMap` uses a combination of a map and linked list to
+maintain amortized O(1) for `Set`, `Get`, `Delete` and `Len`. 
+
+See the full documentation at
+[https://godoc.org/github.com/elliotchance/orderedmap](https://godoc.org/github.com/elliotchance/orderedmap).

go.mod

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+module github.com/elliotchance/orderedmap
+
+go 1.12
+
+require github.com/stretchr/testify v1.4.0

go.sum

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+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
+github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
+gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=

orderedmap.go

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+package orderedmap
+
+import "container/list"
+
+type orderedMapElement struct {
+	key, value interface{}
+}
+
+type OrderedMap struct {
+	kv map[interface{}]*list.Element
+	ll *list.List
+}
+
+func NewOrderedMap() *OrderedMap {
+	return &OrderedMap{
+		kv: make(map[interface{}]*list.Element),
+		ll: list.New(),
+	}
+}
+
+// Get returns the value for a key. If the key does not exist, the second return
+// parameter will be false and the value will be nil.
+func (m *OrderedMap) Get(key interface{}) (interface{}, bool) {
+	value, ok := m.kv[key]
+	if ok {
+		return value.Value.(*orderedMapElement).value, true
+	}
+
+	return nil, false
+}
+
+// Set will set (or replace) a value for a key. If the key was new, then true
+// will be returned. The returned value will be false if the value was replaced
+// (even if the value was the same).
+func (m *OrderedMap) Set(key, value interface{}) bool {
+	_, didExist := m.kv[key]
+
+	if !didExist {
+		element := m.ll.PushBack(&orderedMapElement{key, value})
+		m.kv[key] = element
+	} else {
+		m.kv[key].Value.(*orderedMapElement).value = value
+	}
+
+	return !didExist
+}
+
+// Len returns the number of elements in the map.
+func (m *OrderedMap) Len() int {
+	return len(m.kv)
+}
+
+// Keys returns all of the keys in the order they were inserted. If a key was
+// replaced it will retain the same position. To ensure most recently set keys
+// are always at the end you must always Delete before Set.
+func (m *OrderedMap) Keys() (keys []interface{}) {
+	keys = make([]interface{}, m.Len())
+
+	element := m.ll.Front()
+	for i := 0; element != nil; i++ {
+		keys[i] = element.Value.(*orderedMapElement).key
+		element = element.Next()
+	}
+
+	return keys
+}
+
+// Delete will remove a key from the map. It will return true if the key was
+// removed (the key did exist).
+func (m *OrderedMap) Delete(key interface{}) (didDelete bool) {
+	element, ok := m.kv[key]
+	if ok {
+		m.ll.Remove(element)
+		delete(m.kv, key)
+	}
+
+	return ok
+}