Re: Array spread append

Hi On 4/6/23 00:12, Vorisek, Michael wrote: > Hello, > > I would like to open a discussion for > https://github.com/php/php-src/issues/10791 . > > [https://opengraph.githubassets.com/a23cb565cc8acac6a33ecab5d9ee68a46f046a1ffe215501673156e506695430/php/php-src/issues/10791]<https://github.com/php/php-src/issues/10791�� > ����'�����\> > Array spread append · Issue #10791 · php/php-src<u > )�&d mK©�https://github.com/php/php-src/issues/10791> > Description Currently spread operator can be used for almost anything. But not for array > append. I propose the following to be supported: <?php $arr = [1, 2]; $arr2 = [3, 4]; $arr[...] = > $arr2; // ... > github.com > Appending N elements to an array is quite common language usage pattern and I belive it should > be supported natively for shorter syntax, language consistency and performance. > > I am unable to implement it, but I am ready to help with RFC. > > Michael Vorisek > As far as I understand, this is somewhat of a continuation of https://github.com/php/php-src/issues/9881, in which the concern about the array_merge performance was posted. This in turn resulted in this feature proposal if I understand correctly. I think $x = array_merge($x, ...); is probably a common pattern. Creating a new function or a new syntax will make it more difficult for users to know when to use the array_merge approach or when to use the new append approach. I saw the original comments on the array_merge GitHub thread, and read about the optimization difficulty. The reason there's a performance penalty is due the first array always being copied because: - it may be modified (i.e. keys made sequential) - it may be shared in more places However, I think it might be worth adding an optimization for the most common $x = array_merge($x, ...) case. To do this: - we need to check if the array is sequential. For packed array this can be done with HT_IS_WITHOUT_HOLES(). - we need to detect that coding pattern. This can be done by checking if there's a ZEND_ASSIGN after the call that assigns the result to the first passed array variable. - array must not be immutable - array must have refcount 2: once as variable and once as argument I implemented this optimization in the following commit on my fork: https://github.com/nielsdos/php-src/commit/269d547043c9d3c59d7c9d773eb1ef174dcc5c44 For now it's limited to packed arrays, and it's only a proof-of-concept. I'm also not sure if it's 100% correct, I'd need to do some more debugging / testing to know for sure, but I'm short on time now. The performance improvement for the array_merge case in https://github.com/php/php-src/issues/10993#issuecomment-1493166391 is big: 1.32s without my patch, vs 0.008s with my patch I think this could be made more generic, and be cleaned up. But I don't know if something like this is desired in PHP. Kinds regards Niels