Null-coalesce assign should not perform assign if not null

[ncannasse]

The following code:

class Test {
  static function foo(i) {
    var arr = [];
    for( x in 0...i ) {
	var e = arr[x] ??= [];
        trace(e);
    }      
  }
  static function main() {
    trace("Haxe is great!");
    foo(0);
  }
}

Produces the following result:

static foo(i) {
		let arr = [];
		let _g = 0;
		while(_g < i) {
			let x = _g++;
			console.log("Test.hx:6:",arr[x] = arr[x] != null ? arr[x] : []);
		}
}

I would expect instead it to be:

arr[x] != null ? arr[x] : arr[x] = []

So no assign is performed if not null.

[kLabz]

??= implementation seems wrong indeed

The null-coalescing assignment operator ??= assigns the value of its right-hand operand to its left-hand operand only if the left-hand operand evaluates to null. The ??= operator doesn't evaluate its right-hand operand if the left-hand operand evaluates to non-null.

fc68ea4

[Simn]

Note for the implementation: this should not array-read twice, so we need a temp var and turn it into { var tmp = arr[x]; tmp != null ? tmp : arr[x] = []; }.

This might make it worthwhile to have a distinct block-level case where it simply becomes if (arr[x] == null) arr[x] = [].