Go语言学习记录之一，返回指针与返回值的区别

先来一个返回指针的测试,结果跟想象一样

type A map[int]string
type B struct {
        A
        c int
}

func main() {
        b := B{make(A), 10}
        NewB := func() *B {
                return &b
        }
        c := NewB()
        c.c = 100
        c.A[1] = "3"
        fmt.Println(b, c)
}
/* output
{map[1:3] 100} &{map[1:3] 100}
*/

再试试直接返回值，这下的输出和想象中不一样了

type A map[int]string
type B struct {
        A
        c int
}

func main() {
        a := B{make(A), 10}
        b := B{make(A), 10}
        NewB := func() B {
                return b
        }
        c := NewB()
        c.c = 100
        c.A[1] = "3"
        // c[1]="3" invalid operation: c[1] (type B does not support indexing)
        fmt.Println(a, b, c)
}
/* output
{map[] 10} {map[1:3] 10} {map[1:3] 100}
*/

为什么呢，再试试

type A map[int]string
type B struct {
        A
        c int
}

func main() {
        a := make(A)
        NewA := func() A {
                return a
        }
        b := NewA()
        b[1] = "10"
        fmt.Println(a, b)
}
/* output
map[1:10] map[1:10]
*/
这样就编译不过了
func main() {
        a := make(A)
        NewA := func() *A {
                return &a
        }
        b := NewA()
        b[1] = "10" //invalid operation: b[1] (type *A does not support indexing)
        fmt.Println(a, b)
}

go 语言中map,slice都是指针类型，以值的形式返回struct的时候只是把map对应的指针拷贝了