spread operator as arguments and optionals + REST in function parameters throws error

[cevek]

TypeScript Version: 2.0.3

Code

function foo(a?: number, ...args: number[]) {}
foo(...[1,2,3]); // error

var args = [1, 2, 3];
console.log(...args); //error 

[aluanhaddad]

Your program has an error, it is calling foo with arguments that literally do not match the signature. The same is true about the call to console.log. An optional argument does not merge with a rest argument of a compatible element type because it is a syntactic feature and the parameters are passed by position. How can we distinguish the arguments and refer to them in the body of foo without this behavior?

The correct way to call foo by spreading ...args into the second parameter is

foo(undefined, ...args);
console.log(undefined, ...args);

[cevek]

Yeah, I understand that don't match the signature, but ts checker may merge arguments if you use spreading

function x(...args: number[]);
function x(a: number, ...args: number[]) {}
x(...[1, 2, 3]); //ok

//this is not correct
console.log(undefined, ...args);

// correct code
console.log(args[0], ...args.slice(1));

[Buslowicz]

I've got a bit similar issue, basically, spread arguments do not translate to multiple arguments.

function test(reg: RegExp, str: string) {
  console.log("abc".replace(reg, str));
}
test(...[ /b/, "d" ]); // TS2346:Supplied parameters do not match any signature of call target.

function test(...args);
function test(reg: RegExp, str: string) {
  console.log("abc".replace(reg, str));
}
test(...[ /b/, "d" ]); // works fine

Pretty annoying, as in pure ES6 it works perfectly :(.

[FremyCompany]

I had the same issue when trying to wrap console.log().

log = function(...args) { console.log(...args) } // typing error here :(

for reference console.log is defined as

Console.log(message?: any, ...optionalParams: any[])

So my code is correct from the type point of view.

[FremyCompany]

How is that a question? Perfectly valid ES6 code throws an error in TypeScript. That's a bug, no a feature.

[mhegazy]

your correct, relabeling. the issue is tracked by #5296

[FremyCompany]

👍