On 6 September 2025 01:47:35 BST, Rob Landers <[email protected]> wrote:
>
>Interesting... but we don’t really have a way to say that a parameter or
>return value must satisfy *any* constraints except that it be of a certain
>type. Hmmm, I guess we have "true" and "false" as values that can be
>returned/accepted by functions — but I think they’re the only ones.
Declaring an enum already declares a type. I wasn't thinking about constraining
on lists of values, just saying that something should be a "set of T" where T
is the enum type.
Relying on integer ops, the result ends up as an int:
enum FooOption: flag { ... }
class Foo {
...
function setOption(FooOption $opt): void { ... }
function getCurrentOptions(): int { ... }
}
With general-purpose generics, you can make that strongly typed:
enum FooOption { ... }
class Foo {
...
function setOption(FooOption $opt): void { ... }
function getCurrentOptions(): Set<FooOption> { ... }
}
A specific EnumBitSet<T> could implement the integer serialisation:
class EnumBitSet<T> extends Set<T> {
function asBitMask(): int { ... }
}
enum FooOption: int { ... }
class Foo {
...
function setOption(FooOption $opt): void { ... }
function getCurrentOptions(): EnumBitSet<FooOption> { ... }
}
$foo = new Foo;
...
$foo->getCurrentOptions()->asBitMask();
With the recently proposed declare-time generics, you'd just need an extra
declaration alongside your enum:
class EnumBitSet<T> extends Set<T> {
function asBitMask(): int { ... }
}
enum FooOption: int { ... }
class FooOptionSet extends EnumSet<FooOption> {
// Can add additional methods here, but don't need to
}
class Foo {
...
function setOption(FooOption $opt): void { ... }
function getCurrentOptions(): FooOptionSet { ... }
}
$foo = new Foo;
...
$foo->getCurrentOptions()->asBitMask();
All the operator overloads or methods for things like intersect, union,
contains, etc could be on the top-level Set<T>, since they don't intrinsically
have anything to do with enums. That's the joy of our enum implementation being
object-based: any algorithm that works on object identity automatically works
on enum cases.
Rowan Tommins
[IMSoP]
