Macro service 

macro_rules! service {
    ($x:ty) => { ... };
}

Registers a service with the inventory.

The argument is the service struct’s path. The struct must have both #[ffi(service)] on the struct and #[ffi] on its impl block. All methods and their types are registered automatically.

#[ffi]
pub enum MyError { General }

#[ffi(service)]
pub struct MyService { count: u32 }

#[ffi]
impl MyService {
    pub fn create() -> ffi::Result<Self, MyError> { ffi::Ok(Self { count: 0 }) }
    pub fn fetch(&self) -> u32 { self.count }
}

pub fn ffi_inventory() -> RustInventory {
    RustInventory::new()
        .register(service!(MyService))
        .validate()
}