CODEWITHSUNDEEP
go
Rob Archibald
Rob Archibald

Reputation: 397

How can I tell if my interface{} is a pointer?

If I have an interface being passed into a function, is there a way to tell if the item passed in is a struct or a pointer to a struct? I wrote this silly test to illustrate what I need to figure out.

type MyStruct struct {
    Value string
}

func TestInterfaceIsOrIsntPointer(t *testing.T) {
    var myStruct interface{} = MyStruct{Value: "hello1"}
    var myPointerToStruct interface{} = &MyStruct{Value: "hello1"}
    // the IsPointer method doesn't exist on interface, but I need something like this
    if myStruct.IsPointer() || !myPointerToStruct.IsPointer() { 
        t.Fatal("expected myStruct to not be pointer and myPointerToStruct to be a pointer")
    }
}

Upvotes: 13

Views: 7706

Answers (3)

ferhatelmas
ferhatelmas

Reputation: 3978

func isStruct(i interface{}) bool {
    return reflect.ValueOf(i).Type().Kind() == reflect.Struct
}

You can test via changing type according to your needs such as reflect.Ptr. You can even get pointed value with reflect.Indirect(reflect.ValueOf(i)) after you ensured it's a pointer.

Addition:

It seems reflect.Value has a Kind method so reflect.ValueOf(i).Kind() is enough.

Upvotes: 12

Sebastien C.
Sebastien C.

Reputation: 4833

You could use the reflect package:

i := 42
j := &i
kindOfJ := reflect.ValueOf(j).Kind()

fmt.Print(kindOfJ == reflect.Ptr)

Upvotes: 3

nouney
nouney

Reputation: 4411

If you know the "real" type of the interface, you can simply use a type switch:

type MyStruct struct {
    Value string
}

func TestInterfaceIsOrIsntPointer(t *testing.T) {
    var myStruct interface{} = MyStruct{Value: "hello1"}
    var myPointerToStruct interface{} = &MyStruct{Value: "hello1"}
    // the IsPointer method doesn't exist on interface, but I need something like this
    switch myStruct.(type) {
       case MyStruct:
           // ok
           break
       case *MyStruct:
           // error here
           break
    }
    switch myPointerToStruct.(type) {
       case MyStruct:
           // error here
           break
       case *MyStruct:
           // ok
           break
    }
}

The code is longer but at least you don't need to use the reflect package.

Upvotes: 3

Related Questions