Generic star projection #3290
Description
Let's say my function accepts a generic class with upper bound type that I do not care about.
interface Bound {}
/**
* @template T of Bound
*/
class Collection {}
/**
* @param Collection<*> $list
*/
function size($list): int
{
return $list->count();
}https://phpstan.org/r/3c37ae59-d50b-4ea3-872f-235f5cf05fc2
(Not) possible workarounds:
If call-site variance would be allowed, this could be also written as:
interface Bound {}
/**
* @template T of Bound
*/
class Collection {}
/**
* @param Collection<out Bound> $list
*/
function size($list): int
{
return $list->count();
}Not working example: https://phpstan.org/r/fe3c4116-a825-45e1-8bab-0ab502497a92
If Collection would accept multiple subtypes of T at the same time, this could be also written as:
interface Bound {}
/**
* @template-covariance T of Bound
*/
class Collection {}
/**
* @param Collection<Bound> $list
*/
function size($list): int
{
return $list->count();
}Working example: https://phpstan.org/r/56bb4ce8-ce3c-4f82-9532-8048a0a9eebe
Great articles about generics (star projection): https://typealias.com/guides/star-projections-and-how-they-work/