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July 3, 2015 12:24
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| // Mutability exercise. | |
| #[cfg(not(second))] | |
| fn do_frob() { | |
| let mut aa = MySource::new(); | |
| { | |
| let mut aaw = aa.get_sink(); | |
| let ff = first::Outer::new(); | |
| ff.frob(&mut *aaw); | |
| aaw.flush(); | |
| } | |
| println!("aa: {:?}", aa.all()); | |
| } | |
| #[cfg(second)] | |
| fn do_frob() { | |
| let mut bb = MySource::new(); | |
| { | |
| second::Outer::new(bb.get_sink()).frob(); | |
| } | |
| println!("bb: {:?}", bb.all()); | |
| } | |
| fn main() { | |
| do_frob(); | |
| } | |
| // A source is initially opened, the type being determined by what is actually | |
| // found on the device. | |
| pub trait Source { | |
| fn get_sink<'a>(&'a mut self) -> Box<Sink + 'a>; | |
| fn all(&self) -> Vec<u32>; | |
| } | |
| // To update, request a sink, `add` with it, and then flush. | |
| pub trait Sink { | |
| fn add(&mut self, item: u32); | |
| fn flush(self: Box<Self>); | |
| } | |
| // A very simple implementation of this. | |
| struct MySource { | |
| items: Vec<u32>, | |
| } | |
| impl MySource { | |
| fn new() -> MySource { | |
| MySource { | |
| items: Vec::new(), | |
| } | |
| } | |
| } | |
| impl Source for MySource { | |
| fn all(&self) -> Vec<u32> { | |
| self.items.iter().cloned().collect() | |
| } | |
| fn get_sink<'a>(&'a mut self) -> Box<Sink + 'a> { | |
| Box::new(MySink { | |
| parent: self, | |
| }) | |
| } | |
| } | |
| pub struct MySink<'a> { | |
| parent: &'a mut MySource, | |
| } | |
| impl<'a> Sink for MySink<'a> { | |
| fn add(&mut self, item: u32) { | |
| self.parent.items.push(item); | |
| } | |
| fn flush(self: Box<Self>) { | |
| // Nothing to do in the example. | |
| } | |
| } | |
| //---------------------------------------------------------------------- | |
| // For example. | |
| // In this first instance, the two structs don't contain the Sink and it gets | |
| // passed around as needed. This works, but the Sink has to be passed all | |
| // around to make things work. | |
| #[cfg(not(second))] | |
| mod first { | |
| use super::*; | |
| pub struct Outer { | |
| other: u32, | |
| } | |
| impl Outer { | |
| pub fn new() -> Outer { | |
| Outer { | |
| other: 1, | |
| } | |
| } | |
| pub fn frob(&self, sink: &mut Sink) { | |
| let inside = Inner::new(); | |
| sink.add(self.other); | |
| inside.frob(sink, self.other + 1); | |
| sink.add(self.other + 2); | |
| } | |
| } | |
| struct Inner { | |
| other: u32, | |
| } | |
| impl Inner { | |
| fn new() -> Inner { | |
| Inner { | |
| other: 100, | |
| } | |
| } | |
| fn frob(&self, sink: &mut Sink, extra: u32) { | |
| sink.add(self.other + extra); | |
| } | |
| } | |
| } | |
| // For this second instance, we wrap up the Sink with inner mutability so that | |
| // it can just be stored directly in the instances. | |
| #[cfg(second)] | |
| mod second { | |
| use super::*; | |
| use std::cell::RefCell; | |
| pub struct Outer<'a> { | |
| other: u32, | |
| sink: RefCell<Box<Sink + 'a>>, | |
| } | |
| impl<'a> Outer<'a> { | |
| pub fn new(sink: Box<Sink + 'a>) -> Outer<'a> { | |
| Outer { | |
| other: 1, | |
| sink: RefCell::new(sink), | |
| } | |
| } | |
| pub fn frob(&self) { | |
| let inside = Inner::new(); | |
| self.use_sink(|| { self.other }); | |
| inside.frob(self, self.other + 1); | |
| self.use_sink(|| { self.other + 2 }); | |
| } | |
| pub fn use_sink<F>(&self, f: F) where F: Fn() -> u32 { | |
| let mut sink = self.sink.borrow_mut(); | |
| sink.add(f()); | |
| } | |
| } | |
| struct Inner { | |
| other: u32, | |
| } | |
| impl Inner { | |
| fn new() -> Inner { | |
| Inner { | |
| other: 100, | |
| } | |
| } | |
| fn frob(&self, outer: &Outer, extra: u32) { | |
| outer.use_sink(|| { self.other + extra }); | |
| } | |
| } | |
| } |
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