assigning literal values to constants

[bonzaiferroni]

I recently imported screeps.d.ts and noticed that there were a few issues related to literal values assigned to game constants. Previously they were declared like this:

declare const SOURCE_ENERGY_CAPACITY: number;

Now they are declared like this:

declare const SOURCE_ENERGY_CAPACITY: 3000;

This caused a lot of compiler errors, here is an example:

let score = SOURCE_ENERGY_CAPACITY;
if (WorldMap.roomTypeFromName(sourcePos.roomName) === ROOMTYPE_SOURCEKEEPER) {
    // TS2322: Type '4000' is not assignable to type '3000'
    score = SOURCE_ENERGY_KEEPER_CAPACITY;
}

I'm curious about the rationale for this specific way of declaring types and what situations that it would help. I'm also wondering if there is some setting that I can use to allow it to understand that I'm aiming for a number type here.

[anisoptera]

I don't have a super strong opinion on this. I think newer versions of TS can actually infer the number type there as being valid.

You can poke it into working by explicitly declaring let score: number, of course.

Not all of the constants are defined this way, and it interferes a lot with actual usage when they are, so as I said, I don't feel super strongly about this. I've previously undone this when it was on the REACTIONS constant (thus making it unindexable by strings), for example.

[bonzaiferroni]

I thought there was probably a setting or a later version that would have this work as intended. If not, I would vote to make the types more general. I'm aware of the let score: number workaround, but this seems superfluous.

To have literal values as types seems a bit counterintuitive which is why I was wondering what situations this might be helpful for. It seems like the utility of a type rests partly in its generalizeability. I'm fully willing to drink the koolaid if there is a neat feature that i'm not aware of.

[Dessix]

Type widening allows expansion of a type outward from the default. If you initialize directly from a narrow type, that variable will be explicitly marked as that type. Implicit and inferred typings are able to be widened automatically.

[pathurs]

When declaring a variable, if instead you are specific as to it's value:

declare var one: 1;

You are telling Typescript, that this variable should ONLY be set to this type/value.

This can also be declared as such:

declare var one: 1 | 2 | 3 | 4;

Which would only through errors if you try to set the variable to anything that is not 1, 2, 3, or 4.

[kriber82]

Disclaimer: I am in no way a typescript expert.
As far as i understand the documentation (https://www.typescriptlang.org/docs/handbook/advanced-types.html) typescript only supports string literals types.
This would be in line with typescripts (2.4.2) output on dist/screeps.d.ts.

[Dessix]

@kriber82 When I added these changes, numeric singleton literals were also accepted.

[kriber82]

@Dessix Your changes were and still are fine, it seems.
The typescript compiler is fine with number literal types.
I just could not find them in the documentation and misread an error my IDE reported for a typescript output.