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Extreme explorations of TypeScript's type system

learningtypescript.com

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Re: Extreme explorations of TypeScript's type system

#2

Post by joshuakgoldberg »

TypeScript's type system is Turing Complete: meaning it has conditional branching (conditional types) and works with an arbitrary huge amount of memory. As a result, you can use the type system as its own programming language complete with variables, functions, and recursion. This blog post is a starting list of a bunch of the shenanigans TypeScript developers have pushed the type system to be able to do.

Re: Extreme explorations of TypeScript's type system

#3

Post by theogravity »

This is a great list. I feel I'm only scratching the surface when it comes to Typescript, and it would be awesome to have a place where we can see advanced examples of Typescript usage like this.

I've seen many projects where the typing is done so well that it can infer and include all the data I've fed into the TS-defined functions / classes, which is great for IDE autocompletion.

Re: Extreme explorations of TypeScript's type system

#4

Post by HyperSane »

theogravity wrote: post #3

This is a great list. I feel I'm only scratching the surface when it comes to Typescript, and it would be awesome to have a place where we can see advanced examples of Typescript usage like this. I've seen many projects where the typing is done so well that it can infer and include all the data I've fed into the TS-defined functions / classes, which is great for IDE autocompletion.

What are some of the projects have done typing that well?

Re: Extreme explorations of TypeScript's type system

#5

Post by sir_pepe »

To try and limit one's use of operations on types, as suggested in the article, is not really great advice in my opinion. Sure, you would not want to actually implement and use a VM in types, but distilling rules about a program into types and then deriving the actual interfaces and signatures from those rules with operations on types? That's quite powerful.

TypeScript's type annotations are really a DSL embedded into JavaScript. And they can, and, depending on the problem at hand, should be treated as such.

Re: Extreme explorations of TypeScript's type system

#6

Post by vore »

sir_pepe wrote: post #5

To try and limit one's use of operations on types, as suggested in the article, is not really great advice in my opinion. Sure, you would not want to actually implement and use a VM in types, but distilling rules about a program into types and then deriving the actual interfaces and signatures from those rules with operations on types? That's quite powerful. TypeScript's type annotations are really a DSL embedded int…

I think it depends how far you go: if you start encoding rules into the type system that are undecidable then you can quickly run into trouble.

Re: Extreme explorations of TypeScript's type system

#7

Post by theogravity »

HyperSane wrote: post #4
theogravity wrote: post #3

This is a great list. I feel I'm only scratching the surface when it comes to Typescript, and it would be awesome to have a place where we can see advanced examples of Typescript usage like this. I've seen many projects where the typing is done so well that it can infer and include all the data I've fed into the TS-defined functions / classes, which is great for IDE autocompletion.

What are some of the projects have done typing that well?

If you're a GraphQL developer, Pothos is the best example - all your user-defined types just fits in it like a glove 99% of the time. It definitely makes the most use of TS generics.

https://pothos-graphql.dev/

(I'm a bit sleepy, so this is the main one I can think of at the moment that I really enjoy using.)

Re: Extreme explorations of TypeScript's type system

#8

Post by sir_pepe »

HyperSane wrote: post #4
theogravity wrote: post #3

This is a great list. I feel I'm only scratching the surface when it comes to Typescript, and it would be awesome to have a place where we can see advanced examples of Typescript usage like this. I've seen many projects where the typing is done so well that it can infer and include all the data I've fed into the TS-defined functions / classes, which is great for IDE autocompletion.

What are some of the projects have done typing that well?

Not really a "project", but TypeScript's own type definitions for the DOM are a great example. Eg. document.createElement returns different subtypes of HTMLElement depending on the string argument (HTML tag name) it gets called with.
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