Function leptos_reactive::signal_prelude::create_selector_with_fn

pub fn create_selector_with_fn<T>(
    cx: Scope,
    source: impl Fn() -> T + Clone + 'static,
    f: impl Fn(&T, &T) -> bool + Clone + 'static
) -> impl Fn(T) -> bool + Clonewhere
    T: PartialEq + Eq + Debug + Clone + Hash + 'static,

Creates a conditional signal that only notifies subscribers when a change in the source signal’s value changes whether the given function is true.

You probably don’t need this, but it can be a very useful optimization in certain situations (e.g., “set the class selected if selected() == this_row_index) because it reduces them from O(n) to O(1).