# Plugin
> Type-Safe, Lazily Evaluated, Plugins for Extensible Types
Plugins provide a consistent interface for mixin methods. You can use a plugin anywhere you would use a "mixin" trait and an implementation.
## Example Usage
```rust
// Define a struct.
struct IntPlugin;
// Map it onto an `i32` value.
impl Assoc<i32> for IntPlugin {}
// Define the plugin evaluation function.
// `Extended` is a type that implements `Extensible`.
impl PluginFor<Extended, i32> for IntPlugin {
fn eval(_: &Extended, _: Phantom<IntPlugin>) -> Option<i32> {
Some(0i32)
}
}
assert_eq!(extended.get::<IntPlugin>().unwrap(), 0i32);
```
To do the same thing with a trait, one could do:
```rust
trait IntProducer {
fn get_int_value(&self) -> Option<i32>;
}
impl IntProducer for Extended {
fn get_int_value(&self) -> Option<i32> {
Some(0i32)
}
}
```
Although using a raw trait is less code, plugins provide the following advantages:
* Automatic caching of values. Calling a method again is a constant time operation! This is particularly useful in pipeline structures where only the extensible object is passed around.
* A consistent interface, which also allows for neater name clash resolution. Two modules that provide `PluginX` can be differentiated using a module prefix.
```
e.get::<mod1::PluginX>();
e.get::<mod2::PluginX>();
```