Crate tracker[−][src]
Expand description
Tracker - track changes to structs efficiently
Tracker is a small crate that allows you to track changes to struct fields.
It implements the following methods for your struct fields:
-
get_#field_name()
Get a immutable reference to your field -
get_mut_#field_name()
Get a mutable reference to your field. Assumes the field will be modified and marks it as changed. -
set_#field_name(value)
Get a mutable reference to your field. Marks the field as changed only if the new value isn’t equal with the previous value. -
update_#field_name(fn)
Update your mutable field with a function or closure. Assumes the field will be modified and marks it as changed.
To check for changes you can call var_name.changed(StructName::field_name())
and it will return a bool.
To reset all previous changes you can call var_name.reset()
.
How it works
Let’s have a look at a small example.
#[tracker::track] struct Test { x: u8, y: u64, } fn main() { let mut t = Test { x: 0, y: 0, // the macro generates a new variable called // "tracker" that stores the changes tracker: 0, }; t.set_x(42); // let's check whether the change was detected assert!(t.changed(Test::x())); // reset t so we don't track old changes t.reset(); t.set_x(42); // same value so no change assert!(!t.changed(Test::x())); }
What happens behind the scenes when you call set_x()
is that a bitflag is set in the tracker field of your struct:
y x tracker: u8 = | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | set_x(42) -> | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | reset() -> | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
As you can see this works pretty efficient. The macro expansion looks like this:
impl Test { pub fn get_x(&self) -> &u8 { &self.x } pub fn get_mut_x(&mut self) -> &mut u8 { self.tracker |= Self::x(); &mut self.x } pub fn update_x<F: Fn(&mut u8)>(&mut self, f: F) { self.tracker |= Self::x(); f(&mut self.x); } pub const fn x() -> u8 { 1 << 0usize } pub fn set_x(&mut self, value: u8) { if self.x != value { self.tracker |= Self::x(); } self.x = value; } }
Further attributes
#[tracker::track] struct Test { #[tracker::do_not_track] a: u8, #[do_not_track] b: u8, #[tracker::no_eq] c: u8, #[no_eq] d: u8, }
You can mark fields as
do_not_track
if you don’t want tracker to implement anything for this fieldno_eq
if the type of the field doesn’t implement PartialEq or tracker should not check for equality when callingset_#field_name(value)
so that even overwriting with the same value marks the field as changed. pub use tracker_macros::track;
Attribute Macros
Implements tracker methods for structs