Generics: code example possibly wrong

[isellsoap]

The comment here https://github.com/chibicode/TypeScript-for-Beginner-Programmers/blob/master/src/lib/snippets.ts#L419 states

// This will fail because the second
// parameter must extend boolean | number,
// but instead it’s string
makePair<number, string>()`

But S extends F (which is number | string), so the statement makePair<number, string>() shouldn’t fail. Am I missing something?

[jussivirtanen]

I was stuck on the exact same thing. My explanation: In our function call (makePair<number, string>()) we define F to be a number, so it can't be a string anymore. That's why S can be either a boolean or a number, but not a string.

[p-syche]

Like @jussivirtanen said, we define F in the function call makePair<number, string>(), and once it's defined it can no longer be anything else but a number. There's no mistake here :)

[isellsoap]

Thanks for the explanation. 👍