notes.md

Tuple Length

The challenge is to create a TypeScript generic Length<T> that takes a tuple T and returns the length of the tuple.

For example, given ['tesla', 'model 3', 'model X', 'model Y'], Length should return 4.

Solution

To solve this challenge, we can leverage the fact that in TypeScript, the length property of a tuple type returns the number of elements in the tuple, and that this number is itself a type.

Here's a simple example to illustrate:

type MyTuple = ['a', 'b', 'c']
type LengthOfMyTuple = MyTuple['length'] // 3

In the above code, MyTuple is a tuple type with three elements, and MyTuple['length'] is a type representing the number 3.

Implementation

To implement the Length<T> generic, we can apply this concept to a generic parameter T.

We'll constrain T to be any array or tuple using T extends readonly any[], and then use the indexed access type T['length'] to get the length of the tuple. This can be done as follows:

type Length<T extends readonly any[]> = T['length']

This code reads as: Length<T> is the length of the tuple T.