Thats not 100% true in TypeScript. TypeScript actually only allows "up-casts" and "down-cast" (but if the type is neither a supertype nor a subtype the compiler will throw an error).

Ya, I often have to write “this as any as T” because I’m using T as a self type.

That’s my understanding too. You just can’t cast types wily Nily.

Nope. This is not how casting works in TypeScript. To get an unsafe cast you have to go via the ‘any’ or ‘unknown’ types.

e.g.

‘foo as unknown as Dog’

There are a few casts that are allowed that I would consider unsafe, particularly around unions of literals or using empty object literals:

  // No error here
  type Animal = 'dog' | 'cat';
  const notAnimal = 'couch' as Animal;

  // No error here either
  type Food = { isSpicy: boolean };
  const empty = {} as Food;

https://www.typescriptlang.org/play/index.html#code/C4TwDgpg...