Thread by @GabrielVergnaud

Implementing a get function that narrows union types and rejects invalid paths is tricky.

But it's doable if you know some type-level programming!

Want to become a #TypeScript expert in 2023?

Here is what you need to know to type this function
👇

First, you need a precise understanding of how assignability works in TypeScript.

Types like `never` or `unknown` are super useful, but often misunderstood!

The second chapter of Type-Level TypeScript covers this in depth (you can read it for free!)

type-level-typescript.com/types-are-just…

Second, you need to know how to manipulate type-level data structures like objects and tuples.

You can learn this by reading chapter 3 and 4 (still free)!

type-level-typescript.com/objects-and-re…

type-level-typescript.com/arrays-and-tup…

Third, you need to know how to parse type-level strings!

Chapters 5, 6, and 7 show you how to use the type system as a full fledged programming language to solve this kind of problems

You'll learn about Conditional Types and how to use the `infer` keyword to pattern-match on types 👉 type-level-typescript.com/conditional-ty…

Write arbitrary loops with Recursive Types 👉 type-level-typescript.com/recursive-types

And use all of this to parse strings! 👉 type-level-typescript.com/template-liter…

Supporting unions of objects is tricky, even lodash's `get` function doesn't handle this case well.

To solve this you'll need a super accurate mental model of the way union types work.

This is exactly what the 8th chapter of Type-Level TypeScript will be about!

Chapter 8 will be out soon, but in the meantime here is a TypeScript Playground with all the code used in the video

👉 typescriptlang.org/play?#code/JYW…

Once you start looking at the type system as a programming language, you realize that this isn't black magic, it's just regular code! Anyone can learn this 🧙‍♂️