Add vtable to ExternalValue

[llogiq]

This is not finished yet, but shows the broad direction to take.

[llogiq]

I now appear to have a problem because the types don't add up.

---- koto_tests::io stdout ----
thread 'koto_tests::io' panicked at 'Error while running test 'reading_a_file': File.read_to_string: Expected File instance as first argument
 --- ../../koto/tests/io.koto - 14:30
    |
 14 |     assert_eq contents, file.read_to_string()
    |                              ^^^^^^^^^^^^^^^^', src/koto/tests/koto_tests.rs:22:21
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

---- koto_tests::threads stdout ----
thread 'koto_tests::threads' panicked at 'Error while running test 'spawn_4_threads_and_join': iterator.each: Thread.join: Expected Thread instance as first argument
 --- ../../koto/tests/threads.koto - 20:19
    |
 20 |       .each |t| t.join()
    |                   ^^^^^^
 --- ../../koto/tests/threads.koto - 21:8
    |
 21 |       .to_tuple()
    |        ^^^^^^^^^^', src/koto/tests/koto_tests.rs:22:21

any pointers where to look next?

[irh]

These functions are expecting a Map that contains an ExternalDataId key with the ExternalValue as the associated value.

In the File case, file_fn is a helper that wraps get_external_instance, which pulls the ExternalValue out of the Map and then downcasts it to the expected type. You'll need to adapt get_external_instance (or add a new helper) to match this approach of having methods on an ExternalValue, I guess the only thing you need to do is the downcasting?

[llogiq]

Thank you, that is very helpful!

[llogiq]

Now this has a test of using an external value, and it actually works! 🎉

[irh]

Nice, congrats! Did you see my post on #65 with an outline of the direction that I think should be taken here? I'd be curious to hear your thoughts.

[irh]

Closed in favour of #73