Enum pharos::Filter

pub enum Filter<Event> where
    Event: Clone + 'static + Send,  {
    Pointer(fn(_: &Event) -> bool),
    Closure(Box<dyn FnMut(&Event) -> bool + Send>),
}

Predicate for filtering events.

This is an enum because closures that capture variables from their environment need to be boxed. More often than not, an event will be a simple enum and the predicate will just match on the variant, so it would be wasteful to impose boxing in those cases, hence there is a function pointer variant which does not require boxing. This should be preferred where possible.

use pharos::*;

let a = 5;

// This closure captures the a variable from it's environment.
// We can still use it as a filter by boxing it with `closure`.
//
// Note: it depends on the circumstances, but often enough, we need to
// annotate the type of the event parameter to the predicate.
//
// For this example we use bool as event type for simplicity, but it works
// just the same if that's an enum.
//
let predicate = move |_: &bool| { a; true };

let filter = Filter::Closure( Box::new(predicate) );

// This one does not capture anything, so it can be stored as a function pointer
// without boxing.
//
let predicate = move |_: &bool| { true };

let filter = Filter::Pointer( predicate );

// You can also use actual functions as filters.
//
fn predicate_function( event: &bool ) -> bool { true }

let filter = Filter::Pointer( predicate_function );

Variants

Pointer(fn(_: &Event) -> bool)

A function pointer to a predicate to filter events.

Closure(Box<dyn FnMut(&Event) -> bool + Send>)

A boxed closure to a predicate to filter events.

Trait Implementations

impl<Event> Debug for Filter<Event> where
    Event: Clone + 'static + Send, 

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

Formats the value using the given formatter.

impl<Event> From<Filter<Event>> for ObserveConfig<Event> where
    Event: Clone + 'static + Send, 

Create a ObserveConfig from a Filter, getting default values for other options.

fn from(filter: Filter<Event>) -> Self

Performs the conversion.