A rest parameter must be of an array type

Asked Feb 22 '19 at 17:07

Active Feb 22 '19 at 17:12

Viewed 4,130 times

I have an odd error where the code below works, however the compiler is giving me an error.

I believe C in ...args: C in both spots is throwing

: A rest parameter must be of an array type. (2370)
: A rest parameter must be of an array type. (2370)
: Type '<A extends string, B extends string, C extends any[], D>(A: A, B: B, fn: (...args: C) => D) => { ...' is not assignable to type 'MakeFromTo'.
  Type '{ [x: string]: { to: { [x: string]: (...args: C) => D; }; }; }' is not assignable to type 'Record<A, { to: Record<B, (...args: C) => D>; }>'. (2322)

Here is the code:

type MethodResult<TFrom extends string, TTo extends string, C extends any[], D> = Record<TFrom, {
  to: Record<TTo, (...args: C) => D>;
}>;
type MakeFromTo = <A extends string, B extends string, C extends any[], D> (A: A, B: B, fn: (...args: C) => D) => MethodResult<A, B, C, D>;
const makeFromTo: MakeFromTo = (A, B, fn) => ({ [A]: { to: { [B]: fn } } });

Using typescript 2.6.2

edited Feb 22 '19 at 17:12

asked Feb 22 '19 at 17:07

ThomasReggi

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What is your version of TS? No error in the Playground… – Paleo Feb 22 '19 at 17:11
Using 2.6.2 Updated question. – ThomasReggi Feb 22 '19 at 17:13
1

@ThomasReggi tuples in rest parameters came along in 3.0. This code uses that feature and will not work below 3.0 – Titian Cernicova-Dragomir Feb 22 '19 at 17:14
Is there no way to propagate the input parameters of a function without using a tuple? – ThomasReggi Feb 22 '19 at 17:19
1

The previous way of doing it was using many overloads.. let me dig up an old answer – Titian Cernicova-Dragomir Feb 22 '19 at 17:21
2

@ThomasReggi This should help: https://stackoverflow.com/questions/49420657/how-to-remove-properties-and-promisify-method-via-mapped-type-in-typescript/49421381#49421381 – Titian Cernicova-Dragomir Feb 22 '19 at 17:21

A rest parameter must be of an array type

0 Answers0