go 指针，interface{},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[]
nil result: map[] &map[]
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