diff --git a/packages/hooks/src/lib.rs b/packages/hooks/src/lib.rs index a5b92a036..8178d4d3d 100644 --- a/packages/hooks/src/lib.rs +++ b/packages/hooks/src/lib.rs @@ -60,6 +60,9 @@ pub mod computed; mod use_on_destroy; pub use use_on_destroy::*; +mod use_const; +pub use use_const::*; + mod use_context; pub use use_context::*; diff --git a/packages/hooks/src/use_const.rs b/packages/hooks/src/use_const.rs new file mode 100644 index 000000000..47ddb1ed2 --- /dev/null +++ b/packages/hooks/src/use_const.rs @@ -0,0 +1,76 @@ +use std::rc::Rc; + +use dioxus_core::prelude::*; + +/// Store constant state between component renders. +/// +/// UseConst allows you to store state that is initialized once and then remains constant across renders. +/// You can only get an immutable reference after initalization. +/// This can be useful for values that don't need to update reactively, thus can be memoized easily +/// +/// ```rust, ignore +/// struct ComplexData(i32); +/// +/// fn Component(cx: Scope) -> Element { +/// let id = use_const(cx, || ComplexData(100)); +/// +/// cx.render(rsx! { +/// div { "{id.0}" } +/// }) +/// } +/// ``` +#[must_use] +pub fn use_const( + cx: &ScopeState, + initial_state_fn: impl FnOnce() -> T, +) -> &UseConst { + cx.use_hook(|| UseConst { + value: Rc::new(initial_state_fn()), + }) +} + +#[derive(Clone)] +pub struct UseConst { + value: Rc, +} + +impl PartialEq for UseConst { + fn eq(&self, other: &Self) -> bool { + Rc::ptr_eq(&self.value, &other.value) + } +} + +impl core::fmt::Display for UseConst { + fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { + self.value.fmt(f) + } +} + +impl UseConst { + pub fn get_rc(&self) -> &Rc { + &self.value + } +} + +impl std::ops::Deref for UseConst { + type Target = T; + + fn deref(&self) -> &Self::Target { + self.value.as_ref() + } +} + +#[test] +fn use_const_makes_sense() { + #[allow(unused)] + + fn app(cx: Scope) -> Element { + let const_val = use_const(cx, || vec![0, 1, 2, 3]); + + assert!(const_val[0] == 0); + + // const_val.remove(0); // Cannot Compile, cannot get mutable reference now + + None + } +}