Re: [RFC] Intersection Types

On Thu, Apr 28, 2016 at 4:54 AM, Levi Morrison <levim@php.net> wrote: > Internals, > > As alluded to last week I have another RFC for improving the type > system: [intersection types][1]. > > It allows parameters to define multiple type constraints that must be > satisfied. Common combinations of our built-in types include > ArrayAccess & Traversable & Countable and > Countable & Iterator. > > Some people have suggest I merge this and union types into one RFC. > For now I'll just proceed with them separately to gain feedback. > > [1]: http://wiki.php.net/rfc/intersection_types > > -- > PHP Internals - PHP Runtime Development Mailing List > To unsubscribe, visit: http://www.php.net/unsub.php > To me, it seems that intersection types are more useful than union types (other than the obvious null|Foo and array|Traversable cases) as they'd allow us to write smaller interfaces and better follow ISP in userland, with interfaces becoming much more convenient for documenting the requirements of a parameter. At present we tend to have incomplete implementations of interfaces (e.g. throw OperationNotSupportedException). Union types would allow us to create more, smaller interfaces and avoid situations where the type of a parameter doesn't accurately reflect the method's true requirements, or where concretions are incomplete implementations of an interface. Thanks for your efforts, Levi, I'm excited about this one!