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208 lines
6 KiB
Markdown
208 lines
6 KiB
Markdown
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[![Go Reference](https://pkg.go.dev/badge/github.com/wk8/go-ordered-map/v2.svg)](https://pkg.go.dev/github.com/wk8/go-ordered-map/v2)
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[![Build Status](https://circleci.com/gh/wk8/go-ordered-map.svg?style=svg)](https://app.circleci.com/pipelines/github/wk8/go-ordered-map)
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# Golang Ordered Maps
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Same as regular maps, but also remembers the order in which keys were inserted, akin to [Python's `collections.OrderedDict`s](https://docs.python.org/3.7/library/collections.html#ordereddict-objects).
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It offers the following features:
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* optimal runtime performance (all operations are constant time)
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* optimal memory usage (only one copy of values, no unnecessary memory allocation)
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* allows iterating from newest or oldest keys indifferently, without memory copy, allowing to `break` the iteration, and in time linear to the number of keys iterated over rather than the total length of the ordered map
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* supports any generic types for both keys and values. If you're running go < 1.18, you can use [version 1](https://github.com/wk8/go-ordered-map/tree/v1) that takes and returns generic `interface{}`s instead of using generics
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* idiomatic API, akin to that of [`container/list`](https://golang.org/pkg/container/list)
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* support for JSON and YAML marshalling
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## Documentation
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[The full documentation is available on pkg.go.dev](https://pkg.go.dev/github.com/wk8/go-ordered-map/v2).
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## Installation
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```bash
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go get -u github.com/wk8/go-ordered-map/v2
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```
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Or use your favorite golang vendoring tool!
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## Supported go versions
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Go >= 1.23 is required to use version >= 2.2.0 of this library, as it uses generics and iterators.
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if you're running go < 1.23, you can use [version 2.1.8](https://github.com/wk8/go-ordered-map/tree/v2.1.8) instead.
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If you're running go < 1.18, you can use [version 1](https://github.com/wk8/go-ordered-map/tree/v1) instead.
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## Example / usage
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```go
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package main
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import (
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"fmt"
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"github.com/wk8/go-ordered-map/v2"
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)
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func main() {
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om := orderedmap.New[string, string]()
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om.Set("foo", "bar")
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om.Set("bar", "baz")
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om.Set("coucou", "toi")
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fmt.Println(om.Get("foo")) // => "bar", true
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fmt.Println(om.Get("i dont exist")) // => "", false
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// iterating pairs from oldest to newest:
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for pair := om.Oldest(); pair != nil; pair = pair.Next() {
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fmt.Printf("%s => %s\n", pair.Key, pair.Value)
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} // prints:
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// foo => bar
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// bar => baz
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// coucou => toi
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// iterating over the 2 newest pairs:
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i := 0
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for pair := om.Newest(); pair != nil; pair = pair.Prev() {
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fmt.Printf("%s => %s\n", pair.Key, pair.Value)
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i++
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if i >= 2 {
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break
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}
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} // prints:
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// coucou => toi
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// bar => baz
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}
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```
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An `OrderedMap`'s keys must implement `comparable`, and its values can be anything, for example:
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```go
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type myStruct struct {
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payload string
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}
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func main() {
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om := orderedmap.New[int, *myStruct]()
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om.Set(12, &myStruct{"foo"})
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om.Set(1, &myStruct{"bar"})
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value, present := om.Get(12)
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if !present {
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panic("should be there!")
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}
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fmt.Println(value.payload) // => foo
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for pair := om.Oldest(); pair != nil; pair = pair.Next() {
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fmt.Printf("%d => %s\n", pair.Key, pair.Value.payload)
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} // prints:
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// 12 => foo
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// 1 => bar
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}
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```
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Also worth noting that you can provision ordered maps with a capacity hint, as you would do by passing an optional hint to `make(map[K]V, capacity`):
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```go
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om := orderedmap.New[int, *myStruct](28)
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```
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You can also pass in some initial data to store in the map:
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```go
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om := orderedmap.New[int, string](orderedmap.WithInitialData[int, string](
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orderedmap.Pair[int, string]{
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Key: 12,
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Value: "foo",
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},
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orderedmap.Pair[int, string]{
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Key: 28,
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Value: "bar",
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},
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))
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```
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`OrderedMap`s also support JSON serialization/deserialization, and preserves order:
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```go
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// serialization
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data, err := json.Marshal(om)
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...
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// deserialization
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om := orderedmap.New[string, string]() // or orderedmap.New[int, any](), or any type you expect
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err := json.Unmarshal(data, &om)
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...
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```
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Similarly, it also supports YAML serialization/deserialization using the yaml.v3 package, which also preserves order:
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```go
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// serialization
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data, err := yaml.Marshal(om)
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...
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// deserialization
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om := orderedmap.New[string, string]() // or orderedmap.New[int, any](), or any type you expect
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err := yaml.Unmarshal(data, &om)
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...
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```
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## Iterator support (go >= 1.23)
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The `FromOldest`, `FromNewest`, `KeysFromOldest`, `KeysFromNewest`, `ValuesFromOldest` and `ValuesFromNewest` methods return iterators over the map's pairs, starting from the oldest or newest pair, respectively.
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For example:
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```go
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om := orderedmap.New[int, string]()
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om.Set(1, "foo")
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om.Set(2, "bar")
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om.Set(3, "baz")
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for k, v := range om.FromOldest() {
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fmt.Printf("%d => %s\n", k, v)
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}
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// prints:
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// 1 => foo
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// 2 => bar
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// 3 => baz
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for k := range om.KeysNewest() {
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fmt.Printf("%d\n", k)
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}
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// prints:
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// 3
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// 2
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// 1
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```
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`From` is a convenience function that creates a new `OrderedMap` from an iterator over key-value pairs.
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```go
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om := orderedmap.New[int, string]()
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om.Set(1, "foo")
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om.Set(2, "bar")
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om.Set(3, "baz")
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om2 := orderedmap.From(om.FromOldest())
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for k, v := range om2.FromOldest() {
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fmt.Printf("%d => %s\n", k, v)
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}
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// prints:
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// 1 => foo
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// 2 => bar
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// 3 => baz
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```
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## Alternatives
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There are several other ordered map golang implementations out there, but I believe that at the time of writing none of them offer the same functionality as this library; more specifically:
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* [iancoleman/orderedmap](https://github.com/iancoleman/orderedmap) only accepts `string` keys, its `Delete` operations are linear
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* [cevaris/ordered_map](https://github.com/cevaris/ordered_map) uses a channel for iterations, and leaks goroutines if the iteration is interrupted before fully traversing the map
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* [mantyr/iterator](https://github.com/mantyr/iterator) also uses a channel for iterations, and its `Delete` operations are linear
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* [samdolan/go-ordered-map](https://github.com/samdolan/go-ordered-map) adds unnecessary locking (users should add their own locking instead if they need it), its `Delete` and `Get` operations are linear, iterations trigger a linear memory allocation
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