Rust Plugin Example

main.rs

// I want to create a simple plugin framework for a library I'm writing
// One of the plugins I want to write makes use of a dependency that is very
// restrictive: it enforces the use of references rather than owned values.

trait Modify {
    fn add_one(&mut self);
}

trait Plugin<'a, T>
    where T: Modify
{
    fn get(&'a mut self) -> T;
}

// This is an external dependency and cannot be changed
type AnnoyingDependency<'a> = &'a mut u8;

struct TestPlugin<'a> {
    // this reference is required
    value: AnnoyingDependency<'a>,
}

struct TestModify<'a> {
    test: &'a mut TestPlugin<'a>,
}

impl<'a> Plugin<'a, TestModify<'a>> for &'a mut TestPlugin<'a> {
    fn get(&'a mut self) -> TestModify<'a> {
        TestModify { test: self }
    }
}

impl<'a> Modify for TestModify<'a> {
    fn add_one(&mut self) {
        // Need mutable access to underlying dependency reference here
        *self.test.value += 1;
    }
}

fn main() {
    let mut original = 1;
    
    {
        let mut test = TestPlugin { value: &mut original };
        process(&mut test);
    }

    println!("new value: {}", original);

}

fn process<'a, P, M>(plugin: P) 
    where P: Plugin<'a, M> + 'a, M: Modify
{
    // want to call generic code here 
    let mut inner = plugin.get();
    inner.add_one();
}