Re: Evaluation of constructor arguments if there's no constructor

Julien Pauli wrote (on 14/08/2014):

On Thu, Aug 14, 2014 at 8:26 AM, Tjerk Meesters <tjerk.meesters@gmail.com> wrote:

Hi internals, I was sifting through the bucket o’ bugs and found these two related issues: https://bugs.php.net/bug.php?id=67829 https://bugs.php.net/bug.php?id=54162 (closed) They concern the behaviour of the engine when a class defines no constructor or if the class to be instantiated doesn’t exist, which can be seen here: http://3v4l.org/jOQY0 This is obviously a design decision, but doesn’t seem to have a mention in the documentation nor the spec (I couldn’t find it under the ‘new’ operator). I can add a paragraph in the documentation for it; the question is whether it should also be added to the spec, seeing how HHVM and PHP behave differently in this respect? It could be added as implementation dependent behaviour I suppose?

This is a known behavior which is part of the VM. It is designed at http://lxr.php.net/xref/PHP_5_5/Zend/zend_vm_def.h#3383 I guess its an optimisation that prevents the compiler from compiling a ZEND_DO_FCALL for constructors, which optimizes a bit the VM path for object construction. Dmitry should have more informations. I'm +1 for a documentation or spec mention. Julien.Pauli

When it came up on StackOverflow chat, it was cheekily dubbed "Rasmus evaluation", because nobody could find any theory matching that particular optimisation: https://chat.stackoverflow.com/transcript/11/2013/9/28/14-17 I'm still not entirely sure it's a good idea, and can't imagine how anyone would rely on it (if you have a look at that trasnscript, you'll find some fun attempts at finding an esoteric use). Is it really that big an optimisation that it's worth such surprising behaviour? -- Rowan Collins [IMSoP]