Struct InvocationCount

pub struct InvocationCount { /* private fields */ }

Counts the number of invocations of a function.

The constructor with_fn constructs the metric and a counted function which is used in place of the original function. with_fn_mut is for FnMut functions.

The record and store methods take a Never type and cannot be called directly, instead the count is incremented by invoking the counted function.

⚠️ Since many closures and all function pointers are Copy, be careful not to reuse the uncounted original function after creating the metric.

let uncounted_fn = |x: i32| x * 2;
let (metric1, counted_fn) = InvocationCount::with_fn(uncounted_fn);

assert_eq!(uncounted_fn(1), 2); // not counted
assert_eq!(uncounted_fn(2), 4); // not counted

assert_eq!(counted_fn(1), 2);
assert_eq!(counted_fn(2), 4);
assert_eq!(counted_fn(3), 6);

assert_eq!(metric1.value(), 3);

Implementations

impl InvocationCount

pub fn value(&self) -> u64

The number of times the function has been invoked.

pub fn with_fn<F, X, O>(f: F) -> (Self, impl Fn(X) -> O)

where F: Fn(X) -> O,

Creates the metric and a wrapped counted function, where target function is Fn

pub fn with_fn_mut<F, X, O>(f: F) -> (Self, impl FnMut(X) -> O)

where F: FnMut(X) -> O,

Creates the metric and a wrapped counted function, where target function is FnMut

Trait Implementations

impl Clone for InvocationCount

fn clone(&self) -> InvocationCount

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for InvocationCount

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for InvocationCount

fn default() -> InvocationCount

Returns the “default value” for a type.

impl Metric<Never> for InvocationCount

type Output = u64

The type of elements recorded by the metric. For a delta of last vs current, this might be an n-dimentional vector. It typically needs to be an Owned type, rather than a reference.

fn observe_opt(&mut self, _: Never) -> Option<Self::Output>

Similar to observe except None is returned instead of f64::NAN to indicate not enough data collected. Useful if you like

fn observe(&mut self, x: Input) -> f64

where Self::Output: Into<f64>,

Records the value, and return the calculated metric. If there are not enough samples to calculate the metric, f64::NAN is returned, which will always compare false. So a tolerance check observe(x) < 0.0001 will fail until enough samples have been collected. If you don’t like NANs, then Metric::observe_opt is your friend.

impl StatefulMetric<Never> for InvocationCount

fn store(&mut self, _: Never)

Stores the value, and likely discards older values.

fn value_opt(&self) -> Option<Self::Output>

The calculated value.

fn observe_opt(&mut self, x: Input) -> Option<Self::Output>

fn value(&self) -> f64

where Self::Output: Into<f64>,

The calculated value.