Use runtime check instead compile time for Array#flat

[MaxGraey]

• I've read the contributing guidelines

[MaxGraey]

Solved most of problems. But found another edge case:

export class ArrayArrayI32 extends Array<Array<i32>> {}

Which print errors:

ERROR TS2469: The '>' operator cannot be applied to type '~lib/array/Array<i32>'.

       return (a: T, b: T): i32 => (i32(a > b) - i32(a < b));
                                        ~~~~~
   in ~lib/util/sort.ts(41,38)

ERROR TS2322: Type '~lib/array/Array<i32>' is not assignable to type 'i32'.

       return (a: T, b: T): i32 => (i32(a > b) - i32(a < b));
                                        ~~~~~
   in ~lib/util/sort.ts(41,38)

...

Which is make sense but I'm wondering could we also handle this case? Perhaps add some helpter like hasOperator<">">()?

[dcodeIO]

What happens in this case?

[MaxGraey]

#1353 (comment)

But it's expected due to Array hasn't comparison operators < and >

[dcodeIO]

I see, hmm. Perhaps if we had a better standard than @operator, like using unique symbols, one could check with isDefined. Looks like this isn't easily solvable right now and requires a follow-up PR anyway, though.

[MaxGraey]

I guess it could be solved something like this:

function comparator<T>(a : T, b: T): i32 {
   if (hasOperator<T>("<") && hasOperator<T>(">")) {
      return i32(a > b) - i32(a < b);
   } else {
      throw new TypeError("type hasn't comparison operators");
   }
}

[MaxGraey]

Looks like this isn't easily solvable right now and requires a follow-up PR anyway, though.

Yes, definitely it's for separate PR

[dcodeIO]

Merged this so we have a fix for the reported use case already. Let's think about improving the other cases in a follow-up :)

[github-actions]

🎉 This PR is included in version 0.12.4 🎉

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[jtenner]

Turns out that some compile time checks aren't all that clever :)

[HerrCai0907]

@MaxGraey Do you think it can be reverted now because I have tried in the current compiler. It can pass the compile:

class MyArray extends Array<Array<u8>> {}

export function _start(): void {
  let a = new MyArray();
  a.push([1])
  a.push([2,3]);
  let b = a.flat();
}

[MaxGraey]

Yeah, I guess we could revert this. PR are welcomed