pub trait UpdateInput:
Named
+ HashValue
+ Clean {
type Update;
// Required method
fn update_mut(&mut self, update: Self::Update);
}Expand description
Describe how to update an InputNode value, and how that mutates the internal state. Correct implementation of this trait requires that any temporary state tracked is cleared up when implementing Clean.
§Example
It’s not uncommon for a node which wraps a (potentially large) collection to want to provide dependent nodes an accessor to know which of those have changed since this node was last resolved. Correct implementation of that pattern requires implementation of Clean.
pub struct MyNode {
// Appends every item to this collection.
all_things: Vec<i32>,
// An index where the 'new' items start.
new_things_index: usize,
}
impl UpdateInput for MyNode {
type Update = i32;
fn update_mut(&mut self, input: Self::Update) {
self.all_things.push(input)
}
}
impl MyNode {
// Provide a convenience for dependees to iterate only the new things.
pub fn just_the_new_things_thanks(&self) -> impl Iterator<Item = i32> + '_ {
(self.new_things_index..).map_while(|idx| self.all_things.get(idx).copied())
}
}
impl Clean for MyNode {
fn clean(&mut self) {
// Ensure nothing is yielded next time.
self.new_things_index = self.all_things.len();
}
}
let mut node = MyNode::default();
// Add some initial data
node.update_mut(5);
assert_eq!(
node.just_the_new_things_thanks().collect::<Vec<_>>(),
vec![5]
);
// After cleaning, any temporary state is flushed.
node.clean();
assert_eq!(
node.just_the_new_things_thanks().collect::<Vec<_>>(),
vec![]
);
// Only the latest values are shown.
node.update_mut(7);
node.update_mut(6);
assert_eq!(
node.just_the_new_things_thanks().collect::<Vec<_>>(),
vec![7, 6]
);
// Just to hammer home the point.
node.clean();
assert_eq!(
node.just_the_new_things_thanks().collect::<Vec<_>>(),
vec![]
);In the example above, if Clean wasn’t implemented, the new
values would be displayed to dependent nodes after this node had been
cleaned. This is an unsound implementation, which violates the caching logic
of depends.
Required Associated Types§
Required Methods§
fn update_mut(&mut self, update: Self::Update)
Dyn Compatibility§
This trait is not dyn compatible.
In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.