V: Cannot use interface in array

[netmute]

V version: V 0.1.21 99e0771
OS: macOS 10.14.6

What did you do?

interface Reader {
  name() string
}

fn foo(arr []Reader) {
}

What did you expect to see?
I can pass an array of structs that implement the interface to foo().

What did you see instead?

error: subscript of pointer to incomplete type 'Reader' (aka 'struct Reader')
 Reader arr = ((Reader *) tmp5 . ...
(Use `v -g` to print the entire error message)

V error: C error. This should never happen. Please create a GitHub issue

[teggotic]

That's not a bug. Array of interfaces are not implemented yet. WIP

[medvednikov]

Well that's still a bug :)

[pr0g]

I've been playing around with V recently (I really really like it by the way! 😄) and was hunting for this...

I came across this blog post with the syntax for how it's implemented in Go - http://golangtutorials.blogspot.com/2011/06/polymorphism-in-go.html

type Vehicle interface {
    move() string
}

type Car struct {
}

type Plane struct {
}

func (c Car) move() string {
    return "drive"
}

func (p Plane) move() string {
    return "fly"
}

p := new (Plane)
c := new (Car)

vehicles := [...]Vehicle{p, c}

I was trying to attempt something like this in V but wasn't able to - glad this is just something that's still in the works. Is this on a road map anywhere? Do you imagine it working in a similar way?

Keep up the awesome work! 👍

[medvednikov]

Yes, interfaces are broken right now. They will be fixed in early November.

[pr0g]

Awesome, thanks for the information!

[alexesprit]

It was partially fixed.

Here is an example where the issue is still present:

Summary (Click to expand)

struct Dog {
    breed string
}

fn (d Dog) name() string {
    return 'Dog'
}

fn  main() {
    dog := Dog{}
    // get_name(dog) // uncommenting this line makes the example working
    get_names([dog, dog])
}

fn get_names(speakers []Speaker) {
    for s in speakers {
        println(s.name())
    }
}

interface Speaker {
    name() string
}

[spytheman]

The last example is fixed in 8caf382 . The first one is also no longer a problem.