# ABI SINGLETION
This is a simple ABI singleton Trait helper crate. When you need a trait that only one implementation can exist, you can use this crate.
## Example
A lib crate define a trait that only one implementation exist, you can use it with out `<T>` like code.
```rust
#[api_trait]
pub trait Cat {
fn eat(food: Food) -> usize;
}
/// Only one kind of cat, so no need to known type with `<T>`.
pub fn cat_eat(food: Food) -> usize {
//`CatImpl` is auto generated.
CatImpl::eat(food)
}
```
A crate implements the trait and.
```rust
struct BlackCat;
// There is only one black cat in the world.
#[api_impl]
impl Cat for BlackCat {
fn eat(food: Food) -> usize {
println!("black cat eat one");
food.count - 1
}
}
fn main() {
let food = Food { count: 3 };
println!("There are {} food", food.count);
let left = cat_eat(food);
println!("food left: {}", left);
}
```
## Usage
See `test_project` in this repo for examples.
## Limitations
Only C FFI func support, `self` fields are not supported.