GO_Map_05

Map declaration

m := map[string]int{
    
    "one": 1, "two": 2, "three": 3}
m1 := map[string]int{
    
    }
m1["one"] = 1
m2 := make(map[string]int, 10 /*Initial Capacity*/)

func TestInitMap(t *testing.T) {
    
    
	m1 := map[int]int{
    
    1: 1, 2: 4, 3: 9}
	t.Log(m1[2])
	t.Logf("len m1=%d", len(m1))
	m2 := map[int]int{
    
    }
	m2[5] = 16
	t.Logf("len m2=%d", len(m2))
	m3 := make(map[int]int, 10)
	t.Logf("len m3=%d", len(m3))

}

Access to Map elements

Differences from other major programming languages
​​When the accessed Key does not exist, a zero value will still be returned, and nil cannot be returned to determine whether an element exists

if v, ok := m["four"]; ok {
    
    
t.Log("four", v)
} else {
    
    
t.Log("Not existing")
}

// map不存在key测试  不存在key 取值为0, 判断是否存在key ok:=m1[3]
func TestAccessNotExistingKey(t *testing.T) {
    
    
	m1 := map[int]int{
    
    }
	t.Log(m1[1])
	m1[2] = 0
	t.Log(m1[2])
	m1[3] = 0
	// v, ok:=m1[3]; v: m1[3]   ok: 判断map是否存在该key 存在返回true 反之false
	if v, ok := m1[3]; ok {
    
    
		t.Logf("Key 3 value is %d", v)
	} else {
    
    
		t.Logf("Key 3 is not existing")
	}
}

Map traversal

// map 遍历
func TestTravelMap(t *testing.T) {
    
    
	m1 := map[int]int{
    
    1: 2, 2: 4, 3: 8, 4: 16}
	for k, v := range m1 {
    
    
		t.Log(k, v)
	}
}

Map and factory pattern

• The value of Map can be a method
• Together with Go's Dock type interface, it is convenient to implement the factory pattern of a single method object

Implement Set

There is no Set implementation in Go's built-in collection, you can map[type]bool

1. uniqueness of elements
2. basic operation
   1. add element
   2. Determine whether an element exists
   3. delete element
   4. number of elements

package _map

import "testing"

// - Map的value可以是一个方法
func TestMapWithFunValue(t *testing.T) {
    
    
	m := map[int]func(op int) int{
    
    }
	m[1] = func(op int) int {
    
    
		return op
	}

	m[2] = func(op int) int {
    
    
		return op * op
	}
	m[3] = func(op int) int {
    
    
		return op * op * op
	}
	t.Log(m[1](1), m[2](2), m[3](3))
}

// set
func TestMapForSet(t *testing.T) {
    
    
	mSet := map[int]bool{
    
    }
	mSet[1] = true
	//n := 1 // map_ext_test.go:27: 1 is existing
	n := 3 // map_ext_test.go:30: 3 is not existing
	if mSet[n] {
    
    
		t.Logf("%d is existing", n)
	} else {
    
    
		t.Logf("%d is not existing", n)
	}
	mSet[3] = true
	t.Log(len(mSet)) // map_ext_test.go:33: 2
	delete(mSet, 1)
	n = 1 // map_ext_test.go:39: 1 is not existing
	if mSet[n] {
    
    
		t.Logf("%d is existing", n)
	} else {
    
    
		t.Logf("%d is not existing", n)
	}
}

PS: study notes, invade and delete!