Function freya::prelude::use_comparer

pub fn use_comparer<R>(f: impl FnMut() -> R + 'static) -> Comparer<R>where
    R: Eq + Hash,

Creates a new Comparer which efficiently tracks when a value changes to check if it is equal to a set of values.

Generally, you shouldn’t need to use this hook. Instead you can use crate::use_memo. If you have many values that you need to compare to a single value, this hook will change updates from O(n) to O(1) where n is the number of values you are comparing to.

use dioxus::prelude::*;
use dioxus_signals::*;

fn App(cx: Scope) -> Element {
    let mut count = use_signal(cx, || 0);
    let comparer = use_comparer(cx, move || count.value());

    render! {
        for i in 0..10 {
            // Child will only re-render when i == count
            Child { active: comparer.equal(i) }
        }
        button {
            // This will only rerender the child with the old and new value of i == count
            // Because we are using a comparer, this will be O(1) instead of the O(n) performance of a selector
            onclick: move |_| count += 1,
            "Increment"
        }
    }
}

#[component]
fn Child(cx: Scope, active: ReadOnlySignal<bool>) -> Element {
    if *active() {
        render! { "Active" }
    } else {
        render! { "Inactive" }
    }
}