Hacker News Reader

Comment by jedimastert | Hacker News Reader

> The list of integers could be replaced by using tuples and reading their lengths to do basic arithmetic.

Is that anything like church encoding?

https://www.wikiwand.com/en/Church_encoding#/Church_numerals

Not really. In the Typescript type system tuple types are array types where the length is encoded in the type system. Tuple types can be “added” by concatenation to produce a new tuple type:

    type two = [0, 0]
    type three = [0, 0, 0]
    type five = [...two, ...three]
    type TupleToNumber<T extends any[]> = T[“length”]
    const num: TupleToNumber<five> = 5

Am I understanding this correctly that typescript provides a type-level property on tuples called `"length"`?

yep!

To clarify, the "tuple" is just an array with fixed length. So ts isn't "providing" the length property, it's simply surfacing the underlying Array#length in JS, which it knows to be a constant.

Reply on news.ycombinator.com