Orderly Iteration of Go Maps: A Comprehensive Guide
Iterating through a Go map in order can be a challenge due to the language's仕様, which emphasizes concurrency rather than order preservation. This article will explore two solid methods for achieving ordered iteration while maintaining the advantages of using maps.
1. Maintaining Order with a Keys Slice
This method involves keeping track of map keys in a separate slice to ensure the order of iteration. While introducing an overhead, this approach offers simplicity and clear implementation.
Example Implementation:
type Key int // Key type type Value int // Value type type Map struct { m map[Key]Value keys []Key } func New() *Map { return &Map{m: make(map[Key]Value)} } func (m *Map) Set(k Key, v Value) { if _, ok := m.m[k]; !ok { m.keys = append(m.keys, k) } m.m[k] = v } func (m *Map) Range() { for _, k := range m.keys { fmt.Println(m.m[k]) } }
2. Linking Values in a LinkedList
This approach involves wrapping values in a struct containing the actual value and a reference to the next key. It allows for efficient insertion and removal of elements.
Example Implementation:
type Key int // Key type type Value int // Value type type valueWrapper struct { value Value next *Key // Next key } type Map struct { m map[Key]valueWrapper first, last *Key } func New() *Map { return &Map{m: make(map[Key]valueWrapper)} } func (m *Map) Set(k Key, v Value) { if _, ok := m.m[k]; !ok && m.last != nil { w2 := m.m[*m.last] m.m[*m.last] = valueWrapper{w2.value, &k} } w := valueWrapper{value: v} m.m[k] = w if m.first == nil { m.first = &k } m.last = &k } func (m *Map) Range() { for k := m.first; k != nil; { w := m.m[*k] fmt.Println(w.value) k = w.next } }
Bonus:
Here are some additional tips to consider:
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