Enhancement: Implement UnwrapArrayReduce mutator

[localheinz]

This PR

• Adds new feature UnwrapArrayReduce mutator
• Covered by tests
• Doc PR: Enhancement: Implement UnwrapArrayReduce mutator site#75

Related to #514.

💁‍♂️ Follows the example in #513.

[sidz]

👍

[BackEndTea]

👍

[maks-rafalko]

@sanmai as I remember, you suggested to unwrap the 3rd parameter, not the 1st.

array_reduce($array, $func, $initial) -> $initial

Some thoughts about it:

array_reduce can be used to reduce the whole array to one value (this is how it is defined in the spec: Iteratively reduce the array to a single value using a callback function)

It means that the result of the array_reduce can be not only array, but Object, boolean, number and any other type.

This, in its turn, means that unrapping the 1st argument instead of 3rd can lead to type mismatches, which will immediately lead to incorrectly killed mutant. Example:

- function getSum(array $numbers): int {
-     return array_reduce($numbers, function sum($carry, $item) {
-             $carry += $item;
-             return $carry;
-         },
-         0
-     );
- }

// incorrect mutation
+ function getSum(array $numbers): int {
+     return $numbers; // <---------- array instead of int
+ }

// correct mutation
+ function getSum(array $numbers): int {
+     return 0;
+ }

Probably we can think about all possible cases and produce mutation depending on context, existence of the 3rd parameter, etc.? WDYT?

[sanmai]

Really this has to be about the last argument, not about first as a whole at very least. Sorry about previous review!

[sanmai]

I wonder where I was looking... True, unwrapping the first argument only makes hardly any sense, most of the time it’ll be a definite error.

On the other hand, there’s something about the first argument...

[localheinz]

@borNfreee @sanmai

You are right, this makes a lot of sense!

[localheinz]

Instead of array_key_exists(), would you prefer me to use count()?

[sanmai]

I feel like array_key_exists() is most explicit for a generic case of this mutator.

count() is not such, adds extra limitations.

[sanmai]

First argument opens possibility for an additional mutator:

- array_reduce($array, $func, $initial);
+ $array[0];

I guess this should be a purpose of a different PR.

[maks-rafalko]

👍 👏

[maks-rafalko]

Thank you @localheinz

[localheinz]

Thank you, @BackEndTea, @borNfreee, @sanmai, and @sidz!