String literal types (like Typescript)

1

Hi everyone,
I am looking for a way to constrain a String type to a specific set of strings. In Typescript I make liberal use of string literal types which allow something like this:

type Orientation = "portrait" | "landscapeLeft" | "landscapeRight"

and no other strings would be allowed.

Is that (or something similar) possible in Haxe as well? I find that quite useful for externs to dynamic languages that often use a set of strings to denote distinct categories.

Thanks :slight_smile:

2

enum abstract should do the job:

enum abstract Orientation(String) {
	var portrait;
	var landscapeLeft;
	var landscapeRight;
}

class Main {
	static function draw(orientation:Orientation) {
		trace(orientation);
	}

	static function main() {
		draw(portrait);
	}
}

generated JS:

class Main {
	static draw(orientation) {
		console.log("src/Main.hx:9:",orientation);
	}
	static main() {
		Main.draw("portrait");
	}
}
2 Likes
3

Personally I would rather be explicit about the values of the enum abstract fields, so you can use a proper enum value naming convention (both PascalCase and UPPER_CASE are common in Haxe, but lowerCamelCase looks really strange to me).

enum abstract Orientation(String) {
	var Portrait = "portrait";
	var LandscapeLeft = "landscapeLeft ";
	var LandscapeRight = "landscapeLeft";
}
2 Likes
4

Abstract enums are great!

It would be still nice to have this for Haxe too. You can also define them inline in typescript for example, which is not possible with an enum:

function setOrientation(orientation: "portrait" | "landscape") {
  console.log(orientation);
}
setOrientation("tilted"); 
// Argument of type '"test"' is not assignable to parameter of type '"portrait" | "landscape"
1 Like
5

I cannot agree. It surely looks cute and is useful in the context of TypeScript, because the idea is to add type-safety for JavaScript with its stringly-typing approaches while staying as close to JavaScript syntax as possible (so you can mostly just copy-paste code between languages). But in any other situation IMO this is just gimmicky.

3 Likes
6

Thank you, this is what I was looking for.

(Since I use this feature a lot in TS, I am biased toward making it available in Haxe as well :wink: - it may be gimmicky, but it is also very easy to understand and I like the ergonomics of it, it feels lightweight. Anyway, since I can get what I need with abstract enums, I am happy nonetheless)

7

Great discussion. I’ll be sure to try this sometime.