gistfile1.rs

rustc 0.10-pre (0a5138c 2014-03-04 13:16:41 -0800)


pub trait Expr<'a, T> {
	fn then(&'a self, f: &'a 'a ||) -> T;
}

impl<'a> Expr<'a, ()> for () {
	fn then(&'a self, f: &'a 'a ||) -> () {
		(*f)();
	}
}

pub struct Action<'a> {
	f: Option<&'a 'a ||>,
	next: Option<&'a Action<'a>>,
}

impl<'a> Action<'a> {
	pub fn new(f: &'a 'a ||) -> Action<'a> {
		Action { f: Some(f), next: None }
	}

	pub fn run(&self) {
		match self.next {
			Some(action) => action.run(),
			None => {},
		}

		match self.f {
			None => {},
			Some(f) => (*f)(),
		};
	}
}

impl<'a> Expr<'a, Action<'a>> for Action<'a> {
	fn then(&'a self, f: &'a 'a ||) -> Action<'a> {
		Action { f: Some(f), next: Some(self) }
	}
}

pub fn main() {
	let x = || println!("Hello!");
	let y = || println!("Again!");
	let z = || println!("So...");

	().then(&x).then(&y).then(&z);

	Action::new(&x).then(&y).then(&z).run();
}


Compiler error:
impl2.rs:46:2: 46:4 error: cannot infer an appropriate lifetime for region in type/impl due to conflicting requirements
impl2.rs:46 	().then(&x).then(&y).then(&z);
            	^~
impl2.rs:48:2: 48:26 note: first, the lifetime must be contained by the method call at 48:1...
impl2.rs:48 	Action::new(&x).then(&y).then(&z).run();
            	^~~~~~~~~~~~~~~~~~~~~~~~
impl2.rs:48:2: 48:17 note: ...so that method receiver is valid for the method call
impl2.rs:48 	Action::new(&x).then(&y).then(&z).run();
            	^~~~~~~~~~~~~~~
impl2.rs:46:10: 46:12 note: but, the lifetime must also be contained by the expression at 46:9...
impl2.rs:46 	().then(&x).then(&y).then(&z);