Decrement mutator makes array indexes negative

[maks-rafalko]

Question	Answer
Infection version	0.16
Test Framework version	any
PHP version	x.y.z (php -v)

This should not happen

10) /SourceClass.php:14    [M] DecrementInteger

--- Original
+++ New
@@ @@
         $c = [1, 2, 3];
-        $d = $c[0];
+        $d = $c[-1];

[sanmai]

Negative indexes in an array are not forbidden. You can totally have an array with a negative index.

[maks-rafalko]

right, but from my experience with this mutator, each time it decrements 0 to -1 as an index of the array, it leads to undefined index notice

Notice: Undefined offset: -1

which in its turn always leads to killed Mutant.

So, I think this is a useless mutation in almost 100% cases. I'm speaking only about 0 to -1, not about -99 to -100.

In other words, I propose to not do such mutation if:

• the number is an index of the array
• the number is 0

[LoopKarma]

thank you for labelling issues - I will try to pick up this bug +)
@maks-rafalko can you please explain why mutation should not be applied if the number is an index of the array?

[maks-rafalko]

sure, as I said:

from my experience with this mutator, each time it decrements 0 to -1 as an index of the array, it leads to undefined index notice

Notice: Undefined offset: -1

So, there are many cases when I have similar code to this:

$items = $object->getItems();

Assert::greaterThan(0, $items); // here we know that there is at least 1 item

$firstItem = $items[0];

So, when we have a list of items (array indexed from 0 to N) - there is no point in mutating 0 to -1, because it will always lead to

Notice: Undefined offset: -1

In other words, rephrasing my previous comment, we should not do a mutations from 0 to -1 when: the number is an index of the array AND the number is 0