Our first look at INFER - Type Challenges #4

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[rgolea]

I did this by doing type First<TArray extends any[]> = TArray extends { length: 0 } ? never: TArray[0]. But the infer explanation is really really helpful. Thank you!

[dchroninger]

I just wanted to say thanks for posting awesome and digestible TS content. I'm looking forward to going through your advanced course when it's available. I feel like the barrier to learning how to build "Library world" types is immensely more challenging than learning TS as a user.

[michrisoft]

I saw an answer that was just "T extends Array<never> ? never : T[0];" that works which is pretty interesting because an empty array must be treated as Array<never>. That might be a pretty useful short syntax for handling that case.

[fredcal]

Whenever I feel that I already know enough TS I come back here and realize I'm just like Jon Snow, I know nothing. Thanks for that Matt.

[gulneckm.]

Since I knew of T[0] from last time, this was simple "= T extends [] ? never : T[0];"
Dunno if anything can extend [] (but in that case I probably can reverse the order).

But I managed to sneak infer into TupleToObject and get my recursion 😋

[nght]

Cool! Thank you! Waiting for other type challenges :)

[bluesbr]

I used this one:
type First<TTuple extends readonly any[]> = TTuple['length'] extends 0 ? never : TTuple[0];

It's always been difficult for me to grasp when I can use infer. Thank you so much for this explanation :)

[alihussnain]

I love the way you describe and solve the problem that it hits your mind directly and make everything understandable!!
Keep it up 👍

[FurryDanOriginal]

I did something very similar with

type First<Ts extends unknown[]> = Ts extends []
? never
: Ts[0] | (Ts extends [unknown, ...unknown[]]
? never
: undefined
);

with the main difference being, that if the array is not a tuple, but an unknown length (T[]) I thought it would make sense to return `T | undefined` instead of never, as it may or may not hold a first element.

[istvanagoston]

Thank you for the enjoyable and informative videos, they've also saved a lot of time for me. Keep doing your cool stuff!

[yassinebouchoucha]

the summer is ending soon, when your course on advanced Typescript will be released !?

[matheusviniciusandrade]

Hey Matt, I'm in love with your videos and learning a lot because tbh I''
m not a big fan of TS but I'm giving it a chance. So, I couldn't remember an example in other languages and I'm not sure if this behavior is only in TS, but it seems to be something like => You're creating a feature or functionality just specifying a type? In other languages we need to call a function that belongs to a class, e.g List<string> in Java we have List.first or List.at(0). I'm trying to get used with this way to create functionalities via defining a type, it's pretty weird to me because type should just be a type.

[MrBatocko]

Actually, this doesn't work for me when i declare a const array and use it as follows: First<typeof arrayVariableName>. It always resolves to never. Btw, thanks for high quality materials, they really help a lot!

[kilo.ironblossom]

never is like 'imaginary number' of typescript

[PeterParker-nhdi]

A simpler version is:

type First <TArray extends any[]> = TArray extends [] ? never : TArray[0]

[cobrax]

type First<T extends any[]> = T extends T["length"] ? T[0] : never - why is this not working? T length is > 0 so its true and should take the first index of T otherwise its never. Can you maybe help me ? The Result of this is always never :/

[themost]

where can i find those exercises? Id like to practice

[claustw]

How would this be used in a project? What can I do with the newly created type?

[JakobBjerrePetersen]

Can anybody point me in the direction to where I can read more about "TArray". I guess it's a concept that you can apply to other stuff than an array. I just can't seem to find anything in the TS documentation.

[ColinRichardson]

Don't want to get banned.. So, I will just say Hello this time.