go 指针(interface{},map)

Posted 2020-09-27 dy blog

func testAddDataToResult() {
	var a map[string]interface{}
	Println(a, &a)
	addDataToResult(a, "aa", "bb")
	Println(a, &a)
}
func addDataToResult(result map[string]interface{}, key string, val interface{}) {
	if result == nil {
		Println("nil result:", result, &result)
		result = map[string]interface{}{key: val}
		//result[key] = val
		Println("nil result:", result, &result)
		return
	}
	result[key] = val
	Println("result:", result, &result)
}
结果

map[] &map[]
nil result: map[] &map[]
nil result: map[aa:bb] &map[aa:bb]
map[] &map[]

 

	var a map[string]interface{}
	Println(a, &a)
	addDataToResult(a, "aa", "bb")
	Println(a, &a)
}
func addDataToResult(result map[string]interface{}, key string, val interface{}) {
	if result == nil {
		Println("nil result:", result, &result)
		//result = map[string]interface{}{key: val}
		result[key] = val
		Println("nil result:", result, &result)
		return
	}
	result[key] = val
	Println("result:", result, &result)
}
结果
map[] &map[]
nil result: map[] &map[]
panic: assignment to entry in nil map

　　

func testAddDataToResult() {
	var a = map[string]interface{}{}
	Println(a, &a)
	addDataToResult(a, "aa", "bb")
	Println(a, &a)
}
func addDataToResult(result map[string]interface{}, key string, val interface{}) {
	if result == nil {
		Println("nil result:", result, &result)
		//result = map[string]interface{}{key: val}
		result[key] = val
		Println("nil result:", result, &result)
		return
	}
	result[key] = val
	Println("result:", result, &result)
}
结果
map[] &map[]
result: map[aa:bb] &map[aa:bb]
map[aa:bb] &map[aa:bb]

　　

第一个测试将nil值的map[string]interface{}传到函数，修改后原函数里的值没改变

第二个测试将nil值的map[string]interface{}传入到函数，直接result[key]=val，panic: assignment to entry in nil map

 第三个测试将不为nil值的map[string]interface{}传入到函数，直接result[key]=val，原函数的map被改变了

func testAddDataToResult() {
	var a interface{}
	Println(a, &a)
	addDataToResult(a, "aa", "bb")
	Println(a, &a)
}
func addDataToResult(result interface{}, key string, val interface{}) {
	if result == nil {
		Println("nil result:", result, &result)
		result = map[string]interface{}{key: val}
		Println("nil result:", result, &result)
		return
	}
	result.(map[string]interface{})[key] = val
	Println("result:", result, &result)
}
结果
<nil> 0xc42000e280
nil result: <nil> 0xc42000e290
nil result: map[aa:bb] 0xc42000e290
<nil> 0xc42000e280