I've also seen a work in progress around built-ins collections : php.net/manual/fr/class.ds-collect..., might be the next step over Sets, Maps and others useful collections like the one Python provide.
I've seen it also, but it is a pecl extension (working with PHP 7). I doubt it will become core soon.
Too bad, I feel PHP diserve those built-ins, kind of like they are doing for strictly typed variables...
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