How to use source.last_metadata with list.iter?

[vitoyucepi]

Before 2.0.2 I used on_metadata callback to store metadata into ref().
In 2.0.2 last_metadata was added, but it's not clear how to process it.

a=blank()
print(a.last_metadata()) # OK 
list.iter(print, a.last_metadata()) # Fail

Also why is it nullable? This differs from on_metadata callback argument.

[toots]

It is nullable because it's possible the source never produced any metadata, in which case it will be null. In on_metadata, we do have a metadata at hand when calling the handler.

print can print any value so, it always works even with null values. You can add a default value to nullable types using the ?? operator so, this would work:

list.iter(print, (a.last_metadata() ?? []))

[vitoyucepi]

No this doesn't work as expected.

# a=blank()
;;
a :
  source(audio=?internal(?A), video=?internal(?B), midi=?internal(?C))
  .{
    time : () -> float,
    shutdown : () -> unit,
    fallible : bool,
    skip : () -> unit,
    seek : (float) -> float,
    is_active : () -> bool,
    is_up : () -> bool,
    log : 
    {level : (() -> int?).{set : ((int) -> unit)}
    },
    self_sync : () -> bool,
    duration : () -> float,
    elapsed : () -> float,
    remaining : () -> float,
    on_track : ((([string * string]) -> unit)) -> unit,
    on_leave : ((() -> unit)) -> unit,
    on_get_ready : ((() -> unit)) -> unit,
    on_shutdown : ((() -> unit)) -> unit,
    on_metadata : ((([string * string]) -> unit)) -> unit,
    last_metadata : ((() -> [string * string]?)) -> unit,
    is_ready : () -> bool,
    id : (() -> string)
  } =
  <source>.{time = <fun>, shutdown = <fun>, fallible = false, skip = <fun>, seek = <fun>, is_active = <fun>, is_up = <fun>, log = {level = <fun>.{set = <fun>}}, self_sync = <fun>, duration = <fun>, elapsed = <fun>, remaining = <fun>, on_track = <fun>, on_leave = <fun>, on_get_ready = <fun>, on_shutdown = <fun>, on_metadata = <fun>, last_metadata = <fun>, is_ready = <fun>, id = <fun>}
# a.last_metadata()
;;
- : ((() -> [string * string]?)) -> unit = null
# list.iter(print, (a.last_metadata() ?? []))
;;
At line 5, char 39-41:

Error 5: this value has type
  (...) -> [_]
but it should be a subtype of
  (...) -> (_) -> _

[toots]

Damn. Confirmed, this is a bug in the type declaration on the method. I'll see what I can do, might sneak in a new 2.0.2 tarball with the fix..

[toots]

This should be fixed with the latest v2.0.2 builds and in main as well.