Vector defaultValue argument

[RblSb]

Should fix #8040 and unblock #8495

[Simn]

I'm worried about code generation on static targets because the argument is optional. In particular, we have to make sure that this[i] = defaultValue does not unwrap Null<T> on each iteration as that would cause a big performance hit.

[RblSb]

Some way to unwrap it before iteration, like final value:T = cast value?
In other case Vector probably can be generated as {array: [], length: 123} on js (only 10% slower for array access, but requires more work for other methods). Or filled with nulls (50% slower, still fine).

[back2dos]

Adding optional arguments is technically a breaking change. Also I'm having trouble imagining that new Vector(1000000) has the same performance characteristics on JS with this change. I wonder if having a fill method that returns the vector itself won't do the trick while avoiding all sorts of issues.

[RblSb]

In what cases this is breaking change?
Not against Vector.fill, but i think access performance should be fixed for new Vector too, and initilization performance mean less for storage of fixed size (static targets fill the vector anyway). Some opinions about my ideas above?

[RealyUniqueName]

It's a breaking change because of a signature change. But that's not important because Vector.new is probably never used as a closure.
But having a loop for 100000 iterations inside of new Vector(100000) is important.

[back2dos]

Sorry, forgot to respond.

It's a breaking change because of a signature change. But that's not important because Vector.new is probably never used as a closure.

I was thinking of allocation pools, which doesn't seem that far fetched. But yeah, it's probably not going to affect anyone.

---

I would propose this:

abstract Vector<T> {
  public function new(size:Int):Void;
  public function fill(value:T):Void;// exercise for the writer
  static public function prefilled<T>(size:Int, value:T):Vector<T> {
    #if xyz
      /* fancy xyz-specific magic here */
    #else // default implementation
      var ret = new Vector(size);
      ret.fill(value);
      return ret;
    #end
  }
}

[Simn]

I'm closing this because I don't think having the Vector constructor loop over its length is acceptable. I'd be fine with adding a separate fill method as suggested, that might be useful in various situations anyway.