mirror of
https://github.com/DioxusLabs/dioxus
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60 lines
2.4 KiB
Rust
60 lines
2.4 KiB
Rust
//! Support for storing lazy-nodes on the stack
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//!
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//! This module provides support for a type called `LazyNodes` which is a micro-heap located on the stack to make calls
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//! to `rsx!` more efficient.
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//!
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//! To support returning rsx! from branches in match statements, we need to use dynamic dispatch on [`ScopeState`] closures.
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//!
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//! This can be done either through boxing directly, or by using dynamic-sized-types and a custom allocator. In our case,
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//! we build a tiny alloactor in the stack and allocate the closure into that.
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//!
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//! The logic for this was borrowed from <https://docs.rs/stack_dst/0.6.1/stack_dst/>. Unfortunately, this crate does not
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//! support non-static closures, so we've implemented the core logic of `ValueA` in this module.
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use smallbox::{smallbox, space::S16, SmallBox};
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use crate::{innerlude::VNode, ScopeState};
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/// A concrete type provider for closures that build [`VNode`] structures.
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///
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/// This struct wraps lazy structs that build [`VNode`] trees Normally, we cannot perform a blanket implementation over
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/// closures, but if we wrap the closure in a concrete type, we can use it for different branches in matching.
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///
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///
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/// ```rust, ignore
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/// LazyNodes::new(|f| f.element("div", [], [], [] None))
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/// ```
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pub struct LazyNodes<'a, 'b> {
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inner: SmallBox<dyn FnMut(&'a ScopeState) -> VNode<'a> + 'b, S16>,
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}
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impl<'a, 'b> LazyNodes<'a, 'b> {
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/// Create a new [`LazyNodes`] closure, optimistically placing it onto the stack.
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///
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/// If the closure cannot fit into the stack allocation (16 bytes), then it
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/// is placed on the heap. Most closures will fit into the stack, and is
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/// the most optimal way to use the creation function.
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pub fn new(val: impl FnOnce(&'a ScopeState) -> VNode<'a> + 'b) -> Self {
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// there's no way to call FnOnce without a box, so we need to store it in a slot and use static dispatch
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let mut slot = Some(val);
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Self {
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inner: smallbox!(move |f| {
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let val = slot.take().expect("cannot call LazyNodes twice");
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val(f)
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}),
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}
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}
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/// Call the closure with the given factory to produce real [`VNode`].
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///
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/// ```rust, ignore
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/// let f = LazyNodes::new(move |f| f.element("div", [], [], [] None));
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///
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/// let node = f.call(cac);
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/// ```
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#[must_use]
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pub fn call(mut self, f: &'a ScopeState) -> VNode<'a> {
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(self.inner)(f)
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}
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}
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