i am trying to expand the fruity crate's interop abilities with objective-c collections such as NSArray. collections in objective-c are like generics in other languages: type erasure means that the contained objects are not strongly typed, though one can generally assured that all the items in a collection are of a particular class (in objective-c parlance).
still, the fruity crate aims to make things more type safe on the rust side of things. therefore, it would be best for the rust-side NSArray type to be parameterized with a type.
in fruity, there is a macro for declaring objective-c classes called objc_subclass (it subclasses NSObject). this macro matches a definition of the class that aims to inherit from rust struct definition grammar (presumably for ergonomics).
thus, it translates something like pub class MyObject<'a> : NSObject<'a> into an appropriate rust struct definition.
it currently supports lifetimes on the input. i need to extend it to support a generic type, but am having trouble getting the macro to match a generic T.
it is currently written as:
macro_rules! subclass {
(
$(#[$meta:meta])+
$vis:vis class $a:ident $(<$lifetime:lifetime>)? : $b:ty ;
) => {
$(#[$meta])+
#[repr(C)]
$vis struct $a $(<$lifetime>)? ($b);
i have tried replacing $lifetime:lifetime with a number of different patterns, but i get compiler errors of various kinds.
what is the appropriate way to match and then re-use the type parameters? i need to match them optionally, so either zero, one, or two parameters (lifetime and generic type specifier). do i need to replicate the match arm for each one?