help-rust/README.md

## setup

In module `modules`, I have:

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

In module `filters`, I have:

```rust
pub struct Equals { … }

impl Equals {
  pub fn from_args(mut args: ModuleArgs) -> Equals {
    Equals { … }
  }
}

impl Module for Equals {
  fn run(&self, record: &mut Record) -> Result<bool, ()> { … }
}
```

## goal, “naive-style”

What I really want (for a start) is that, in module `modules`:

```rust
struct Available {
  name: String,
  cons: Box<fn(ModuleArgs) -> dyn Module>
}

const available: [Available] = [
  Available { name: "equals", cons: Box.new(filters::Equals::from_args) }
];
```

with `available` being an array of available modules, each having a name and a constructor.

## problem

The above code gives me these errors (which I suspect are hiding the next error about `"equals"` probably being `&str` instead of `String`…):

* first:

  ```
  error[E0423]: expected value, found struct `Box`
    --> src/modules.rs:10:37
     |
  10 |   Available { name: "equals", cons: Box.new(filters::Equals::from_args) }
     |                                     ^^^ constructor is not visible here due to private fields
  ```

* second:

  ```
  error[E0277]: the size for values of type `[modules::Available]` cannot be known at compilation time
   --> src/modules.rs:9:18
    |
  9 | const available: [Available] = [
    |                  ^^^^^^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `std::marker::Sized` is not implemented for `[modules::Available]`
  ```