32 lines
964 B
Rust
32 lines
964 B
Rust
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use core::cell::UnsafeCell;
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pub struct LazyCell<T> {
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contents: UnsafeCell<Option<T>>,
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}
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impl<T> LazyCell<T> {
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pub fn new() -> LazyCell<T> {
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LazyCell {
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contents: UnsafeCell::new(None),
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}
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}
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pub fn borrow(&self) -> Option<&T> {
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unsafe { &*self.contents.get() }.as_ref()
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}
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pub fn borrow_with(&self, closure: impl FnOnce() -> T) -> &T {
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// First check if we're already initialized...
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let ptr = self.contents.get();
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if let Some(val) = unsafe { &*ptr } {
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return val;
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}
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// Note that while we're executing `closure` our `borrow_with` may
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// be called recursively. This means we need to check again after
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// the closure has executed. For that we use the `get_or_insert`
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// method which will only perform mutation if we aren't already
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// `Some`.
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let val = closure();
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unsafe { (*ptr).get_or_insert(val) }
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}
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}
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