With current versions of TypeScript, this is an error:
((_) => {})(...[null]); // ERROR: Expected 1 arguments, but got a minimum of 0.In order to make this code work, the developer needs to tell the type checker to shut up, which could look like this:
(((_) => {}) as any)(...[null]); // Working fine.This is unfortunate, as passing arguments for functions around in tuples is a common pattern in functional programming and there is currently no way to do it safely in TypeScript.
This was mentioned in #5296, which lead to the spread operator being supported for arrays. Supporting tuples in addition to arrays is not a straightforward change, since tuples can currently have additional values, which are not type checked (there is proposal #6229, which aims to fix this):
function f(s: string, a: number, b: number, c: number, ...rest: number[]) {
// ...
}
// legal
let quad: [string, number, number, number, number] = ["foo", 1,2,3,4];
f(...quad); // and triple
quad = ["foo", 1, 2, 3, 4, "boo!"]; // it is legal currently
f(...quad); // now it blows up in run time because rest has a stringHere is a longer and more detailed example taken from #5296 showing the desired behavior in detail:
function f(s: string, a: number, b: number, c: number, ...rest: number[]) {
// ...
}
function g(s: string, a: number, b: number) {
}
// legal
let quad: [string, number, number, number, number] = ["foo", 1,2,3,4];
let triple: [string, number, number, number] = ["foo", 1,2,3];
let double: [string, number, number] = ["foo", 1,2];
f(...quad); // and triple
f(...double, 3);
f("foo", ...[1,2,3]);
f(...quad, 1, ...[1,2,3]); // and triple
g(...double);
// illegal
f(...double); // too short -- double doesn't match parameter 'c'
g(...triple); // too many parameters
g(...quad); // too many parameters
With current versions of TypeScript, this is an error:
In order to make this code work, the developer needs to tell the type checker to shut up, which could look like this:
This is unfortunate, as passing arguments for functions around in tuples is a common pattern in functional programming and there is currently no way to do it safely in TypeScript.
This was mentioned in #5296, which lead to the spread operator being supported for arrays. Supporting tuples in addition to arrays is not a straightforward change, since tuples can currently have additional values, which are not type checked (there is proposal #6229, which aims to fix this):
Here is a longer and more detailed example taken from #5296 showing the desired behavior in detail: