TypeScript playground: https://www.typescriptlang.org/play?#code/KYDwDg9gTgLgBDAnmY... |
TypeScript playground: https://www.typescriptlang.org/play?#code/KYDwDg9gTgLgBDAnmY... |
Uncomment one of the PGunXX types that you want to see, then below it type this:
const boardstr: PGun10 = ``;
const boardstr: PGun10 = `............................................
........................xx..................
........................x..x................
..........x.x...............x......xx.......
........x...x..xxx..........x......xx.......
.xx.....x...................x...............
.xx....x....x.......xx..x..x................
........x.......x.x..x..xx..................
........x...x.....xxx.......................
..........x.x...............................
............................................`; declare const boardstr: PGun10
// ^?
[0] https://aphyr.com/posts/342-typing-the-technical-interview
[1] https://www.richard-towers.com/2023/03/11/typescripting-the-...
https://aphyr.com/posts/353-rewriting-the-technical-intervie...
These advanced type systems are essentially a form of pre-compile time scripting to assert certain guarantees about user defined types. It's the same mechanism that makes C++ templates turing complete.
[0] https://www.typescriptlang.org/docs/handbook/2/template-lite...
Conditional types are probably rarely used in practial code, but it opens the door for a lot of geekery.
[1] https://www.destroyallsoftware.com/talks/the-birth-and-death...
If anyone else is interested in an internship or full-time position in typescript: https://www.uncountable.com/hiring/hn
Any sufficiently advanced type system is indistinguishable from an interpreter!
type MyType<T> = someFunc(T)
Of course these functions might be typed too…
In college I did it in assembler (a couple hundred bytes of code) on a PDP11/34 and displayed the results on an oscilloscope screen :)
What I'm saying is that if instead we said that all type annotations must follow existing JS grammar rules, with perhaps a couple of small additions, then we'd be able to support all sorts of complex type annotations in JS directly, using existing syntax. This would mean that TS's grammar would end up changing a bit, but that's a small price to pay for ongoing interoperability.
For example, instead of
type UserProperties = keyof typeof User;
type UserProperties = keyOf(typeOf(User));If feeling adventurous, read e.g. https://lpn.swi-prolog.org/lpnpage.php?pagetype=html&pageid=...
that's a great quote.
IIRC the type checker is literally a Prolog.