Typescript arrow function with signature accepts wrong parameter

Question

Consider the type:

type GenericFunction = <T>(props: Array<T>) => void

and the arrow function:

const test: GenericFunction = <X>(props: X) => {
let dd: X }

How come that the test function accepts X as argument although the type GenericFunction defines Array<T> as parameter?

hendra · Accepted Answer · 2021-06-25 07:28:45Z

1

There are types for X that will satisfy the signature of GenericFunction, that's why the compiler does not give an error. Theres is just an implicit constraint now that X must be an array type.

Only if you add a constraint for X that conflicts with this implicit constraint you get an error:

// this gives a compile error
const test: GenericFunction = <X extends number>(props: X) => {};

answered Jun 25, 2021 at 7:28

hendra

2,6515 gold badges24 silver badges39 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

DimitriosP Over a year ago

This is understandable but it looks kind of incorrect to me. For example the test function is going to be called like test<number>(new Array<number>()). So in my mind X in this case represents number and not Array<number>

Collectives™ on Stack Overflow

Typescript arrow function with signature accepts wrong parameter

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related