jpetkau / genrc Goto Github PK

I'm not super happy with the Rcl / Arcl types. Several alternate approaches
are possible but they all have their own tradeoffs.

1. If it was possible to default lifetimes, then Rcl could be named Rc and
   the lifetime param just defaulted to static.
   https://internals.rust-lang.org/t/lifetime-parameter-default-value/1722.
   Maybe someday.

2. type Rc<'a, T> = Genrc<'a, T, ...>, i.e. only have the lifetime-containing
   version. This works fine in normal code, but now you need an explicit
   'static or 'a in any structs containing Rc so it's much less of a
   drop-in replacement, and it's kinda ugly. (Cow<'static, T> has the same
   problem.)

3. Make Rc<T> contain a phantom T instead of a phantom &T, and Rcl<T> a
   completely different type. This makes Rc a better drop-in replacement for
   std::rc::Rc, but means there must be two different Rc::project()
   functions, one that erases the lifetime and one that doesn't, and it's harder
   to write generic code over both.

4. Make the general version Rc<T, L>, replacing the lifetime parameter with
   a type that might have a lifetime, e.g. Rc<i32, &'a i32>. But now the
   type L contains too much info; we really want it to be either () or
   &'a (), but there's no convert an arbitrary lifetime-containing type to
   a minimal type that just expresses the lifetimes.