mirror of
https://github.com/DioxusLabs/dioxus
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84 lines
3.4 KiB
Rust
84 lines
3.4 KiB
Rust
//! Example: Memoization
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//! --------------------
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//!
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//! This example showcases how memoization works in Dioxus.
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//!
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//! Memoization is the process in which Dioxus skips diffing child components if their props don't change.
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//! In React, components are never memoized unless wrapped in `memo` or configured with `shouldComponentUpdate`.
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//!
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//! Due to the safety guarantees of Rust, we can automatically memoize components in some circumstances. Whenever a
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//! component's properties are valid for the `'static` lifetime, Dioxus will automatically compare the props before
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//! diffing the component. If the props don't change (according to PartialEq), the component will not be re-rendered.
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//!
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//! However, if the props use some generics or borrow from their parent, then Dioxus can't safely supress updates,
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//! and is forced to render the child. If you think that this behavior is wrong for your usecase, you can implement
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//! the memo method yourself, but beware, doing so is UNSAFE and may cause issues if you do it wrong.
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//!
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//! If you want to gain that little bit extra performance, consider using global state management, signals, or
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//! memoized collections like im-rc which are designed for this use case.
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use dioxus::prelude::*;
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// By default, components with no props are always memoized.
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// A props of () is considered empty.
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pub fn Example(cx: Scope) -> Element {
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cx.render(rsx! {
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div { "100% memoized!" }
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})
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}
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// These props do not borrow any content, and therefore can be safely memoized.
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// However, the parent *must* create a new string on every render.
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// Notice how these props implement PartialEq - this is required for 'static props
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#[derive(PartialEq, Props)]
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pub struct MyProps1 {
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name: String,
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}
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pub fn Example1(cx: Scope<MyProps1>) -> Element {
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cx.render(rsx! {
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div { "100% memoized! {cx.props.name}" }
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})
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}
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// These props do not borrow any content, and therefore can be safely memoized.
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// In contrast with the `String` example, these props use `Rc<str>` which operates similar to strings in JavaScript.
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// These strings cannot be modified, but may be cheaply shared in many places without issue.
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#[derive(PartialEq, Props)]
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pub struct MyProps2 {
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name: std::rc::Rc<str>,
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}
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pub fn Example2(cx: Scope<MyProps2>) -> Element {
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cx.render(rsx! {
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div { "100% memoized! {cx.props.name}" }
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})
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}
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// These props *do* borrow any content, and therefore cannot be safely memoized!.
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#[derive(PartialEq, Props)]
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pub struct MyProps3<'a> {
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name: &'a str,
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}
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// We need to manually specify a lifetime that ensures props and scope (the component's state) share the same lifetime.
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// Using the `pub fn Example(cx: Scope): Component` pattern _will_ specify a lifetime, but that lifetime will be static which might
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// not exactly be what you want
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fn Example3(cx: Scope<'a, MyProps3<'a>>) -> DomTree {
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cx.render(rsx! {
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div { "Not memoized! {cx.props.name}" }
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})
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}
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// These props *do* borrow any content, and therefore cannot be safely memoized!.
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// However, they cannot be compared, so we don't need the PartialEq flag.
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#[derive(Props)]
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pub struct MyProps4<'a> {
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onhandle: &'a dyn Fn(),
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}
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// We need to manually specify a lifetime that ensures props and scope (the component's state) share the same lifetime.
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fn Example4<'a>(cx: Scope<'a, MyProps4<'a>>) -> DomTree {
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cx.render(rsx! {
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div { "Not memoized!", onclick: move |_| (props.onhandle)() }
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})
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}
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