HypeScript: Simplified TypeScript type system in TypeScript's own type system

Post by xsmasher » Fri, Jul 29, 2022, 6:55 PM UTC

mmis1000 wrote: post #75

xsmasher wrote: post #74

Earlier quoted context omitted.

What would you use for a field called "stage" that could be set to 'dev' or 'stage' or 'prod'? Or other enum-type things? I've seen pure JS enums like {'dev' : Symbol('dev'), 'prod' : etc} but I never use them because you can't send them over the wire. You could use a type like {dev:true} | {prod:true} | {stage:true} but you still wind up comparing strings.

> {dev:true} | {prod:true} | {stage:true} This can't be accessed safely. Because all value in typescript can be sub type of how it typed. It means code following will pass. var a = { dev: true, get prod() { throw Error() } } var b: { dev:true } | {prod:true} | {stage:true} = a And there is no guarantee that access any of these fields is safe.

Post by mmis1000 » Sat, Jul 30, 2022, 2:51 AM UTC

xsmasher wrote: post #81

mmis1000 wrote: post #75

Earlier quoted context omitted.

> {dev:true} | {prod:true} | {stage:true} This can't be accessed safely. Because all value in typescript can be sub type of how it typed. It means code following will pass. var a = { dev: true, get prod() { throw Error() } } var b: { dev:true } | {prod:true} | {stage:true} = a And there is no guarantee that access any of these fields is safe.

That did not compile for me with my TS settings; > Type '{ dev: boolean; readonly prod: void; }' is not assignable to type '{ prod: true; }' It's still a bad solution though; it allows nonsense values like {dev:true, prod:true}.