Type error when using RescriptCore flag

1

I was going through the book “Introducing Rescript” and trying out the following code:

@val external process : 'a = "process"
Js.log(`Hello, ${process["argv"][2]}`)
                 ~~~~~~~~~~~~~~~~~~

If I enable RescriptCore I get the error:

This has type: option<'a>
Somewhere wanted: string

The type hint for process[“argv”][2] is {.."argv": array<'a>}

But if I disable RescriptCore there is no error and the type hint shows process[“argv”][2] is {.."argv": array<string>}

So I’m curious as to what about RescriptCore would cause the type to be different? I’m using Rescript v10 (also tried v10.1.4).

2

This is likely because when you have ReScript Core open it’ll call a getter function (Array.get) which returns an option rather throwing if out of bounds.

3

Ah, okay. That makes sense.