使用反射，如何将值设置为结构字段（指针）

Question

I try to set value to a struct field (pointer field) by reflect, but failed.

1. I get the name of a struct field, so use FieldByName to get the field
2. The field is a pointer.
3. I try to use FieldByName().Set FieldByName().SetPointer to set value.

type t struct {
    b *int
}

func main() {
    t := new(ts)
    a := new(int)
    ss := reflect.ValueOf(t).FieldByName("b").Set(a)
}

type t struct {
    b *int
}

func main() {
    t := new(ts)
    a := new(int)
    ss := reflect.ValueOf(t).FieldByName("b").SetPointer(a)
}

First code: =======> ./test.go:14:50: cannot use a (type *int) as type reflect.Value in argument to reflect.ValueOf(t).FieldByName("b").Set ./test.go:14:50: reflect.ValueOf(t).FieldByName("b").Set(a) used as value

Second code: =======> ./test.go:14:57: cannot use a (type *int) as type unsafe.Pointer in argument to reflect.ValueOf(t).FieldByName("b").SetPointer ./test.go:14:57: reflect.ValueOf(t).FieldByName("b").SetPointer(a) used as value

I want to use reflect to make the pointer field (name "b") alloced a space and set a value.

Answer 1

type ts struct {
    B *int    //field must be exported
}

func main() {
    var t ts
    foo := 5
    a := &foo
    //Use Elem() to indirect through the pointer and get struct field
    //Use reflect.ValueOf(a) to satisfy Set() signature
    reflect.ValueOf(&t).Elem().FieldByName("B").Set(reflect.ValueOf(a))
    fmt.Println(*t.B)
}

Playground https://play.golang.org/p/gZt0ahTZMIi