Great idea! I'm all in for the variant with an is_array check. It shall be the most useful.

@sanmai no problem, implemented. The new mutations are:

- $a = [...[1, 2, 3], 4];
+ $a = [[1, 2, 3][0], 4];

- $a = [...$collection, 4];
+ $a = [is_array($collection) ? $collection[0] : iterator_to_array($collection)[0], 4];

- $a = [...getCollection(), 4];
+ $a = [is_array(getCollection()) ? getCollection()[0] : iterator_to_array(getCollection())[0], 4];

I wish iterator_to_array would take arrays, returning arrays as they were! Oh well...

It may be better to use reset() because PHP will happily unroll non-zero indexed arrays.

$array = [1 => 'bar','baz'];
$example = [...$array, 'foo'];

makes sense, updated the code

Unfortunately, reset(arrGen()) produces a notice:

Notice: Only variables should be passed by reference

I see only one solution - introduce a variable:

- $arr = [...arrGen()];
+ $_traversable = arrGen();
+ $arr = [is_array($_traversable) ? reset($_traversable) : reset(iterator_to_array($_traversable)));

UPD:

we can also use array_slice that makes new keys: https://3v4l.org/JKM6J

function getArray() {
    return [1 => 11, 2 => 22];
}

array_slice(getArray(), 0, 1)[0]; // 11

and the diff

- $arr = [...arrGen()];
+ $arr = [array_slice(is_array($_traversable) ? $_traversable : iterator_to_array($_traversable), 0, 1)[0]];

Updated to use array_slice as discussed above. For integer keys, array_slice returns a new array with reset indexes, started from 0 and we safely using array_slice(...)[0].

If the array has string keys, it's not a problem, because spread operator can not work with string keys.

Yes, otherwise put you can't use a spread operator with such an array in the first place.

Do you think this can work?

$a = [[...$collection][0], 4];

Do you think this can work?

$a = [[...$collection][0], 4];

Not sure I got the question. If this is the original code before mutation, then the current state of PR works nice with it:

$collection = [5, 6, 7];

- $a = [[...$collection][0], 4];
+ $a = [[array_slice(is_array($collection) ? $collection : iterator_to_array($collection), 0, 1][0], 4];

which results to

[[5][0], 4]

// and then 

[5, 4]

I'm more about this mutation:

- $a = [...$collection, 4];
+ $a = [[...$collection][0], 4];

- $a = [...getCollection(), 4];
+ $a = [[...getCollection()][0], 4];

If it works, we should be able to cut on array_slice() and so forth.

👏 awesome

Updated the code and added more tests for [...new ArrayIterator(['a', 'b', 'c'])] case from RFC

Appveyor fail is unrelated, see #786

Thank you @sanmai for review and ideas