115 lines
3.6 KiB
Rust
115 lines
3.6 KiB
Rust
use crate::read::Readable;
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use crate::CopyValue;
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use crate::Signal;
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use crate::SignalData;
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use dioxus_core::ScopeId;
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use generational_box::Storage;
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use std::fmt::Debug;
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use std::fmt::Display;
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/// A read only signal that has been mapped to a new type.
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pub struct MappedSignal<U: 'static + ?Sized> {
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origin_scope: ScopeId,
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mapping: CopyValue<Box<dyn Fn() -> U>>,
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}
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impl MappedSignal<()> {
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/// Create a new mapped signal.
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pub fn new<T, S, U>(
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signal: Signal<T, S>,
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mapping: impl Fn(&T) -> &U + 'static,
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) -> MappedSignal<S::Ref<U>>
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where
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S: Storage<SignalData<T>>,
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U: ?Sized,
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{
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MappedSignal {
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origin_scope: signal.origin_scope(),
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mapping: CopyValue::new(Box::new(move || S::map(signal.read(), &mapping))),
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}
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}
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}
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impl<U> MappedSignal<U> {
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/// Get the scope that the signal was created in.
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pub fn origin_scope(&self) -> ScopeId {
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self.origin_scope
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}
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/// Get the current value of the signal. This will subscribe the current scope to the signal.
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pub fn read(&self) -> U {
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(self.mapping.read())()
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}
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/// Run a closure with a reference to the signal's value.
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pub fn with<O>(&self, f: impl FnOnce(U) -> O) -> O {
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f(self.read())
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}
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}
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impl<U: ?Sized + Clone> MappedSignal<U> {
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/// Get the current value of the signal. This will subscribe the current scope to the signal.
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pub fn value(&self) -> U {
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self.read().clone()
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}
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}
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impl<U: ?Sized> PartialEq for MappedSignal<U> {
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fn eq(&self, other: &Self) -> bool {
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self.mapping == other.mapping
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}
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}
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impl<U> std::clone::Clone for MappedSignal<U> {
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fn clone(&self) -> Self {
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*self
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}
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}
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impl<U> Copy for MappedSignal<U> {}
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impl<U: Display> Display for MappedSignal<U> {
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fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
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self.with(|v| Display::fmt(&v, f))
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}
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}
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impl<U: Debug> Debug for MappedSignal<U> {
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fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
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self.with(|v| Debug::fmt(&v, f))
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}
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}
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impl<T> std::ops::Deref for MappedSignal<T> {
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type Target = dyn Fn() -> T;
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fn deref(&self) -> &Self::Target {
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// https://github.com/dtolnay/case-studies/tree/master/callable-types
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// First we create a closure that captures something with the Same in memory layout as Self (MaybeUninit<Self>).
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let uninit_callable = std::mem::MaybeUninit::<Self>::uninit();
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// Then move that value into the closure. We assume that the closure now has a in memory layout of Self.
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let uninit_closure = move || Self::read(unsafe { &*uninit_callable.as_ptr() });
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// Check that the size of the closure is the same as the size of Self in case the compiler changed the layout of the closure.
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let size_of_closure = std::mem::size_of_val(&uninit_closure);
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assert_eq!(size_of_closure, std::mem::size_of::<Self>());
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// Then cast the lifetime of the closure to the lifetime of &self.
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fn cast_lifetime<'a, T>(_a: &T, b: &'a T) -> &'a T {
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b
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}
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let reference_to_closure = cast_lifetime(
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{
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// The real closure that we will never use.
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&uninit_closure
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},
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// We transmute self into a reference to the closure. This is safe because we know that the closure has the same memory layout as Self so &Closure == &Self.
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unsafe { std::mem::transmute(self) },
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);
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// Cast the closure to a trait object.
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reference_to_closure as &Self::Target
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}
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}
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