#change #notify #track #reactive #watch


tracks changes to data and notifies listeners

1 unstable release

Uses old Rust 2015

0.1.0 Jan 6, 2017

#13 in #change


245 lines

data_tracker - tracks changes to data and notifies listeners Version Status Doc


Documentation is available here.


The main API feature is the DataTracker struct, which takes ownership of a value.

The principle of operation is that DataTracker::as_tracked_mut() returns a mutable Modifier. Modifier has two key properties:

  • It implements the DerefMut trait and allows ergonomic access to the underlying data.
  • It implements the Drop trait which checks if the underlying data was changed and, if so, notifies the listeners.

Futhermore, DataTracker::as_ref() returns a (non-mutable) reference to the data for cases when only read-only access to the data is needed.

To implement tracking, when Modifier is created, a copy of the original data is made and when Modifier is dropped, an equality check is performed. If the original and the new data are not equal, the callbacks are called with references to the old and the new values.


use data_tracker::DataTracker;

// Create a new type to be tracked. Must implement Clone and PartialEq.
#[derive(Debug, Clone, PartialEq)]
struct MyData {
    a: u8,

// Create some data.
let data = MyData {a: 1};

// Transfer ownership of data to the tracker.
let mut tracked_data = DataTracker::new(data);

// Register a listener which is called when a data change is noticed.
let key = 0; // Keep the key to remove the callback later.
tracked_data.add_listener(key, Box::new(|old_value, new_value| {
    println!("changed {:?} -> {:?}", old_value, new_value);

    // Create x, a (non-mutable) reference to original data.
    let x = tracked_data.as_ref();
    println!("x.a: {}",x.a);

    // Create x, which allows modifying the original data and checks for changes when
    // it goes out of scope.
    let mut x = tracked_data.as_tracked_mut();
    x.a = 10;
    println!("x.a: {}",x.a);
    // When we leave this scope, changes are detected and sent to the listeners.

// Remove our callback.


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Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

Code of conduct

Anyone who interacts with data_tracker in any space including but not limited to this GitHub repository is expected to follow our code of conduct

No runtime deps