84 lines
2.7 KiB
Rust
84 lines
2.7 KiB
Rust
use core::ops::{Deref, DerefMut};
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#[cfg(any(feature = "use_std", feature = "use_alloc"))]
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use core::borrow::BorrowMut;
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use core::fmt;
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#[cfg(feature = "use_std")]
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use std::boxed::Box;
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#[cfg(feature = "use_alloc")]
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use alloc::boxed::Box;
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#[cfg(feature = "use_std")]
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use std::vec::Vec;
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/// A managed object.
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///
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/// This enum can be used to represent exclusive access to objects. In Rust, exclusive access
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/// to an object is obtained by either owning the object, or owning a mutable pointer
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/// to the object; hence, "managed".
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///
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/// The purpose of this enum is providing good ergonomics with `std` present while making
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/// it possible to avoid having a heap at all (which of course means that `std` is not present).
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/// To achieve this, the `Managed::Owned` variant is only available when the "std" feature
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/// is enabled.
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///
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/// A function that requires a managed object should be generic over an `Into<Managed<'a, T>>`
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/// argument; then, it will be possible to pass either a `Box<T>`, `Vec<T>`, or a `&'a mut T`
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/// without any conversion at the call site.
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pub enum Managed<'a, T: 'a + ?Sized> {
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/// Borrowed variant, either a single element or a slice.
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Borrowed(&'a mut T),
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/// Owned variant, only available with `std` present.
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#[cfg(any(feature = "use_std", feature = "use_alloc"))]
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Owned(Box<BorrowMut<T>>)
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}
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impl<'a, T: 'a + fmt::Debug + ?Sized> fmt::Debug for Managed<'a, T> {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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write!(f, "Managed::from({:?})", self.deref())
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}
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}
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impl<'a, T: 'a + ?Sized> From<&'a mut T> for Managed<'a, T> {
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fn from(value: &'a mut T) -> Self {
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Managed::Borrowed(value)
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}
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}
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#[cfg(any(feature = "use_std", feature = "use_alloc"))]
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impl<T, U: BorrowMut<T> + 'static> From<Box<U>> for Managed<'static, T> {
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fn from(value: Box<U>) -> Self {
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Managed::Owned(value)
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}
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}
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#[cfg(feature = "use_std")]
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impl<T: 'static> From<Vec<T>> for Managed<'static, [T]> {
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fn from(mut value: Vec<T>) -> Self {
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value.shrink_to_fit();
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Managed::Owned(Box::new(value))
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}
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}
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impl<'a, T: 'a + ?Sized> Deref for Managed<'a, T> {
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type Target = T;
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fn deref(&self) -> &Self::Target {
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match self {
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&Managed::Borrowed(ref value) => value,
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#[cfg(any(feature = "use_std", feature = "use_alloc"))]
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&Managed::Owned(ref value) => (**value).borrow()
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}
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}
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}
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impl<'a, T: 'a + ?Sized> DerefMut for Managed<'a, T> {
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fn deref_mut(&mut self) -> &mut Self::Target {
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match self {
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&mut Managed::Borrowed(ref mut value) => value,
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#[cfg(any(feature = "use_std", feature = "use_alloc"))]
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&mut Managed::Owned(ref mut value) => (**value).borrow_mut()
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}
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}
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}
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