CODEWITHSUNDEEP
reflectiongo
Avdept
Avdept

Reputation: 2289

Create new object knowing reflected type

In function, one of arguments I'm passing

reflect.TypeOf(Person)

where person is struct with few strings. If another function which accepts this argument, I want to instantiate this empty struct knowing its reflected type.

I have tried following

ins := reflect.New(typ)  //typ is name or passed reflect.TypeOf(Person)

But this returns me nil. What am I doing wrong?

Upvotes: 2

Views: 188

Answers (1)

icza
icza

Reputation: 417462

To tell what you're doing wrong we should see more of your code. But this is a simple example how to do what you want:

type Person struct {
    Name string
    Age  int
}

func main() {
    p := Person{}

    p2 := create(reflect.TypeOf(p))

    p3 := p2.(*Person)
    p3.Name = "Bob"
    p3.Age = 20
    fmt.Printf("%+v", p3)
}

func create(t reflect.Type) interface{} {
    p := reflect.New(t)
    fmt.Printf("%v\n", p)

    pi := p.Interface()
    fmt.Printf("%T\n", pi)
    fmt.Printf("%+v\n", pi)

    return pi
}

Output (Go Playground):

<*main.Person Value>
*main.Person
&{Name: Age:0}
&{Name:Bob Age:20}

reflect.New() returns a value of reflect.Value. The returned Value represents a pointer to a new zero value for the specified type.

You can use Value.Interface() to extract the pointer.

Value.Interface() returns a value of type interface{}. Obviously it can't return any concrete type, just the general empty interface. The empty interface is not a struct, so you can't refer to any field. But it may (and in your case it does) hold a value of *Person. You can use Type assertion to obtain a value of type *Person.

Upvotes: 2

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