Arithmetic magic methods

[henrique-borba]

I'm currently developing an extension for PHP for matrix calculations but PHP does not have the option of intercepting arithmetic operations using objects. I then decided to update the arithmetic functions in zend_operators.c to work with objects.

Use Case

<?php
class MyArithmeticClass {
    public $value;

    public function __construct($value)
    {
          $this->value = $value;
    }

    public function __add($obj) {
        return new MyArithmeticClass($this->value + $obj->value);
    }
    public function __mul($obj) {
        return new MyArithmeticClass($this->value * $obj->value);
    }
    public function __div($obj) {
        if(is_object($obj)) {
            return new MyArithmeticClass($this->value / $obj->value);
        }
        if(is_long($obj)) {
            return new MyArithmeticClass($this->value / $obj);    
        }
    }
    public function __sub($obj) {
        return new MyArithmeticClass($this->value - $obj->value);
    }
}

$a = new MyArithmeticClass(1);
$b = new MyArithmeticClass(2);

$c = $a * $b * $b / 2;

print_r($c);

MyArithmeticClass Object
(
    [value] => 2
)

These feature is especially relevant for Math and Linear Algebra libraries. Currently, if I want to create a library to multiply and add arrays, it would have to be developed in a way that calls become repetitive and often make a mess:

$a = new CustomArray([1, 2]);
$b = new CustomArray([3, 4]);
$c = $a->add($b)->add(2)->dot($a)->sub($b);

This could be written like:

$a = new CustomArray([1, 2]);
$b = new CustomArray([3, 4]);
$c = $a + ($b + 2) * $a - $b;

Some people however could use these methods to add an object to a collection in a different (maybe bizarre) way:

$people = new People();

$people->add($person);
//  could be written
$people = $people + $person;
// or maybe removing a person from the people collection
$people = $people - $person;

PS: Only an example, I personally would stay with $people::add in this case.

[henrique-borba]

Currently the summation operation with arrays works like concatenation and this is causing the errors. I will fix it.

[nikic]

I'm currently developing an extension for PHP for matrix calculations but PHP does not have the option of intercepting arithmetic operations using objects. I then decided to update the arithmetic functions in zend_operators.c to work with objects.

PHP does support this via the do_operation object handler.

[henrique-borba]

@nikic Thanks a lot! You just solved a nightmare for me, this was essential to my project. I didn't realize the existence of this object handler.

Not wanting to take up too much of your time, but then the implementation would be something like:

static zend_object_handlers my_handler;

ZEND_MINIT_FUNCTION(MyProject)
{
        memcpy(&myproject_object_handlers, &std_object_handlers, sizeof(zend_object_handlers));
        myproject_object_handlers.do_operation = my_do_operation;
}

Is this correct?

Thanks again

[nikic]

@henrique-borba Right, and you will also have to assign your custom object handlers inside your create_object class handler (or create it if you don't have one yet).

You can take a look at ext/gmp for an example of an extension that uses do_operation.

[weltling]

@nikic does do_operation respect the operands order? I remember some discrepancy, or it was an Opcache optimization, so operands for * were swapped. Just asking as the operands order is critical for the matrix math.

Thanks.

[nikic]

@weltling I think there are some opcache optimizations that may swap operand order. We can drop them for ZEND_MUL at least.

[nikic]

I've removed the opcache optimization that I'm aware of in 1165a90. Maybe there are others.

[nikic]

As we already have the do_operation mechanism, I'm going to close this PR. Feel free to ping me if you encounter any problems with it.

[henrique-borba]

Hi @nikic,

Thanks a lot again. I'm happy to see you cared about OPCache swaps. I just realized I must opened an RFC por this kind of change, anyway, I don't think I will do it as your guidance was enough. I realize your OPCache change would only affect PHP next major release (Am I wrong?). Is it possible to detect operand swap before it happens? I would like to make arithmetic operations available for PHP 7.X. I could for example, swap the operands before OPCache swap so theier order will be as expected?

Excuse my english, I refuse using Google Translator haha.

Anyway, thanks a lot. @nikic I'm a big fan of your work, just having your attention is a win. See you.