101 lines
3.3 KiB
Rust
101 lines
3.3 KiB
Rust
use core::ops::{Deref, DerefMut};
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use core::fmt;
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#[cfg(feature = "std")]
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use std::boxed::Box;
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#[cfg(all(feature = "alloc", not(feature = "std")))]
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use alloc::boxed::Box;
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#[cfg(feature = "std")]
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use std::vec::Vec;
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#[cfg(all(feature = "alloc", not(feature = "std")))]
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use alloc::vec::Vec;
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/// A managed slice.
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///
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/// This enum can be used to represent exclusive access to slices of objects.
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/// In Rust, exclusive access to an object is obtained by either owning the object,
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/// or owning a mutable pointer 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 variants other than `Borrowed` are only available when the corresponding
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/// feature is opted in.
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///
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/// A function that requires a managed object should be generic over an `Into<ManagedSlice<'a, T>>`
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/// argument; then, it will be possible to pass either a `Vec<T>`, or a `&'a mut [T]`
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/// without any conversion at the call site.
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///
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/// See also [Managed](enum.Managed.html).
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pub enum ManagedSlice<'a, T: 'a> {
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/// Borrowed variant.
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Borrowed(&'a mut [T]),
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/// Owned variant, only available with the `std` or `alloc` feature enabled.
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#[cfg(any(feature = "std", feature = "alloc"))]
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Owned(Vec<T>)
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}
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impl<'a, T: 'a> fmt::Debug for ManagedSlice<'a, T>
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where T: fmt::Debug {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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match self {
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&ManagedSlice::Borrowed(ref x) => write!(f, "Borrowed({:?})", x),
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#[cfg(any(feature = "std", feature = "alloc"))]
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&ManagedSlice::Owned(ref x) => write!(f, "Owned({:?})", x)
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}
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}
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}
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impl<'a, T: 'a> From<&'a mut [T]> for ManagedSlice<'a, T> {
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fn from(value: &'a mut [T]) -> Self {
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ManagedSlice::Borrowed(value)
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}
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}
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macro_rules! from_unboxed_slice {
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($n:expr) => (
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impl<'a, T> From<[T; $n]> for ManagedSlice<'a, T> {
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#[inline]
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fn from(value: [T; $n]) -> Self {
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ManagedSlice::Owned((Box::new(value) as Box<[T]>).into_vec())
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}
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}
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);
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($n:expr, $( $r:expr ),*) => (
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from_unboxed_slice!($n);
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from_unboxed_slice!($( $r ),*);
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)
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}
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#[cfg(any(feature = "std", feature = "alloc"))]
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from_unboxed_slice!(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
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16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31);
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#[cfg(any(feature = "std", feature = "alloc"))]
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impl<'a, T: 'a> From<Vec<T>> for ManagedSlice<'a, T> {
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fn from(value: Vec<T>) -> Self {
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ManagedSlice::Owned(value)
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}
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}
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impl<'a, T: 'a> Deref for ManagedSlice<'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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&ManagedSlice::Borrowed(ref value) => value,
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#[cfg(any(feature = "std", feature = "alloc"))]
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&ManagedSlice::Owned(ref value) => value
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}
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}
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}
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impl<'a, T: 'a> DerefMut for ManagedSlice<'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 ManagedSlice::Borrowed(ref mut value) => value,
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#[cfg(any(feature = "std", feature = "alloc"))]
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&mut ManagedSlice::Owned(ref mut value) => value
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}
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}
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}
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