help-rust/README.md

## my issue

In module `modules`, I have:

```rust
pub trait Action {
  fn act(&self, record: &mut Record) -> Result<(), ()>;
}

pub trait Filter {
  fn filter(&self, record: &mut Record) -> bool;
}

pub enum ModuleKind { Action, Filter }

pub struct Available {
  name: &'static str,
  kind: ModuleKind,
  cons: fn(ModuleArgs) -> Box<dyn Module>
}

pub enum Module {
  Action(&Action),
  Filter(&Filter)
}

impl Module {
  fn run(&self, record: &mut Record) -> Result<bool, ()> {
    match self {
      Module::Action(a) => match a.act(record) {
        Ok(()) => Ok(true),
        Err(()) => Err(())
      },
      Module::Filter(f) => Ok(f.filter(record))
    }
  }
}
```

To give some context, I intend to use `Available` with the [Inventory](https://crates.io/crates/inventory) crate: each module will register itself, either as a “Filter” or as an “Action”.

The 2 things I do not like in this code are:

* I feel like there is redundancy between the `Module` enum and the `ModuleKind` enum.
* I need, that:
    - an `Available` with `kind` being a `ModuleKind::Action` has a `cons` that produces a `Module::Action`
    - an `Available` with `kind` being a `ModuleKind::Filter` has a `cons` that produces a `Module::Filter`

  or even better, that I could read the variant produced by `cons`, and `kind` wouldn’t be needed any more.