@val, does it do anything?

1

I’ve been getting better acquainted with interop bindings and I noticed that @val, which is throughout the documentation, doesn’t seem to matter. Every example binding I’ve found works fine after removing it. What dumb thing am I not noticing?

2

Is this some regression or accidental feature of v10.0.0, perhaps?

I get warnings like this in ReScript 9 when I remove any @val, e.g.:
Unimplemented primitive used:resolved

See playground (switch to v9 on settings tab)

cc @cristianoc @Hongbo

3
5

Ok I see this breaking change for 10.0.0, but I’m on 10.0.1. Whatever the problem, I wish I had waited a few weeks to look into bindings, I wouldn’t have been so confused :wink:

Externals without @val annotations do not work anymore, and externals with = "" give an error.

  • Example: external setTimeout: (unit => unit, int) => float = "setTimeout" is not supported anymore.
  • Fix: use @val external setTimeout: (unit => unit, int) => float = "setTimeout" instead.
  • Example2: @val external setTimeout: (unit => unit, int) => float = "" is not supported anymore.
  • Fix2: use @val external setTimeout: (unit => unit, int) => float = "setTimeout" instead.
6

But the external (at least in my playground example) still works without @val in V10?

Edit: I literally copied the first example that “is not supported anymore” from the Changelog into the playground and it works:
https://rescript-lang.org/try?code=KYDwLsBOB2CGA2ACAzsMAVAlgW2AewFcwAuRACgOkzEQF4A+RS6gGkU2jAEo7GAzeHlg1aiAESoMOfETEAoOfDSJYdFGiy5CYMmR4NEAKWQA6QQHMyYsNPbJE2gIRiuXOcbN5LsN0A

@cristianoc

7

IIRC, It is there for historical reasons. ReScript (or BuckleScript) used to require it to make it different from C style externals to avoid ambiguity, since we decided to focus on JS only, such restrictions are lifted at some time

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