Argument removal mutators

[sanmai]

There is a lot of functions in PHP that take a variable number of arguments. They ought to be mutated. For example, like so:

- $basket = array_replace($base, $replacements, $replacements2);
+ $basket = array_replace($base, $replacements);

And:

- $basket = array_replace($base, $replacements, $replacements2);
+ $basket = array_replace($base, $replacements2);

Obviously these have to be yield mutators, as implemented in #450, or planned to be implemented in #494. Similarly to #514 these mutators may enjoy own separate profile.

• array_replace() Enhancement: Implement ArgumentRemovalArrayReplace mutator #565
• array_diff()
• array_merge()
• ...

[localheinz]

@sanmai

What do you think, should we remove all combinations? For example

$merged = array_merge($a, $b, $c);

becomes

$merged = array_merge($a);
$merged = array_merge($b);
$merged = array_merge($c);
$merged = array_merge($a, $b);
$merged = array_merge($a, $c);
$merged = array_merge($b, $c);

?

[sanmai]

These are almost duplicates to what a mutator from #514 will do.

$merged = array_merge($a);
$merged = array_merge($b);
$merged = array_merge($c);

E.g. the latter is same as $merged = $c with a sole exception of array_merge being used for its renumbering side-effect. But against that side-effect $merged = $c mutation is even better. So, yeah, there got to be a solid case for these mutations to exist. I can't think of one yet.

These below look totally sensible to me:

$merged = array_merge($a, $b);
$merged = array_merge($a, $c);
$merged = array_merge($b, $c);

[sanmai]

Using all possible combinations of arguments not only somewhat burdensome to implement and test, but also can lead to an exponential growth of mutants to tests. Say, you have an array_merge() call with 5 arguments. That's 15 combinations... Or 2 ** n - 1 for n=4, speaking of formulas. For 10 arguments, if we'd happen to find them, which is not an impossible event, it'll be 1023 extra mutant to test, just out of the thin air, for a single mutator. Now consider if we add a couple of such mutators... Will they all worth it? Hard to say.

So I think best would be not to diverge into things exponential and keep to removal of arguments, only, for time being.

On a side note, I can't remember if we can add comment nodes, yet think we should be able to, but commenting out a removed argument seems prettier than just to remove:

-$merged = array_merge($a, $b, $c);
+$merged = array_merge($a, /*$b,*/ $c);