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use std::ops::Deref;
use std::rc::Rc;
use yew::prelude::*;
/// State handle for the [`use_default`] hook.
pub struct UseDefaultHandle<T> {
inner: UseStateHandle<Option<T>>,
default: Rc<T>,
}
impl<T> UseDefaultHandle<T>
where
T: 'static,
{
/// Replaces the value.
pub fn set(&self, value: Option<T>) {
self.inner.set(value);
}
}
impl<T> Deref for UseDefaultHandle<T> {
type Target = T;
fn deref(&self) -> &Self::Target {
let value = &(*self.inner);
value.as_ref().unwrap_or_else(|| self.default.as_ref())
}
}
impl<T> Clone for UseDefaultHandle<T> {
fn clone(&self) -> Self {
Self {
inner: self.inner.clone(),
default: self.default.clone(),
}
}
}
impl<T> PartialEq for UseDefaultHandle<T>
where
T: PartialEq,
{
fn eq(&self, other: &Self) -> bool {
*self.inner == *other.inner
}
}
/// A state hook that returns the default value when state is None.
///
/// # Example
///
/// ```rust
/// # use yew::prelude::*;
/// #
/// use yew_hooks::prelude::*;
///
/// #[function_component(UseDefault)]
/// fn default() -> Html {
/// let state = use_default(|| None, "Hello(default)".to_string());
///
/// let onclick = {
/// let state = state.clone();
/// Callback::from(move |_| {
/// state.set(Some("World!".to_string()));
/// })
/// };
///
/// let onclear = {
/// let state = state.clone();
/// Callback::from(move |_| {
/// state.set(None);
/// })
/// };
///
/// html! {
/// <>
/// <button {onclick}>{ "Set to World!" }</button>
/// <button onclick={onclear}>{ "Clear" }</button>
/// <b>{ "Current value: " }</b>
/// { &*state }
/// </>
/// }
/// }
/// ```
#[hook]
pub fn use_default<T, F>(init_fn: F, default: T) -> UseDefaultHandle<T>
where
T: 'static,
F: FnOnce() -> Option<T>,
{
let inner = use_state(init_fn);
let default = use_memo((), |_| default);
UseDefaultHandle { inner, default }
}