| use core::ops::{Deref, DerefMut}; |
| use core::fmt; |
| |
| #[cfg(feature = "std")] |
| use std::boxed::Box; |
| #[cfg(all(feature = "alloc", not(feature = "std")))] |
| use alloc::boxed::Box; |
| #[cfg(feature = "std")] |
| use std::vec::Vec; |
| #[cfg(all(feature = "alloc", not(feature = "std")))] |
| use alloc::vec::Vec; |
| |
| /// A managed object. |
| /// |
| /// This enum can be used to represent exclusive access to objects. In Rust, exclusive access |
| /// to an object is obtained by either owning the object, or owning a mutable pointer |
| /// to the object; hence, "managed". |
| /// |
| /// The purpose of this enum is providing good ergonomics with `std` present while making |
| /// it possible to avoid having a heap at all (which of course means that `std` is not present). |
| /// To achieve this, the variants other than `Borrow` are only available when the corresponding |
| /// feature is opted in. |
| /// |
| /// A function that requires a managed object should be generic over an `Into<Managed<'a, T>>` |
| /// argument; then, it will be possible to pass either a `Box<T>`, `Vec<T>`, or a `&'a mut T` |
| /// without any conversion at the call site. |
| /// |
| /// Note that a `Vec<T>` converted into an `Into<Managed<'a, [T]>>` gets transformed |
| /// into a boxed slice, and can no longer be resized. See also |
| /// [ManagedSlice](enum.ManagedSlice.html), which does not have this drawback. |
| pub enum Managed<'a, T: 'a + ?Sized> { |
| /// Borrowed variant. |
| Borrowed(&'a mut T), |
| /// Owned variant, only available with the `std` or `alloc` feature enabled. |
| #[cfg(any(feature = "std", feature = "alloc"))] |
| Owned(Box<T>) |
| } |
| |
| impl<'a, T: 'a + ?Sized> fmt::Debug for Managed<'a, T> |
| where T: fmt::Debug { |
| fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| match self { |
| &Managed::Borrowed(ref x) => write!(f, "Borrowed({:?})", x), |
| #[cfg(any(feature = "std", feature = "alloc"))] |
| &Managed::Owned(ref x) => write!(f, "Owned({:?})", x) |
| } |
| } |
| } |
| |
| impl<'a, T: 'a + ?Sized> From<&'a mut T> for Managed<'a, T> { |
| fn from(value: &'a mut T) -> Self { |
| Managed::Borrowed(value) |
| } |
| } |
| |
| #[cfg(any(feature = "std", feature = "alloc"))] |
| impl<'a, T: ?Sized + 'a> From<Box<T>> for Managed<'a, T> { |
| fn from(value: Box<T>) -> Self { |
| Managed::Owned(value) |
| } |
| } |
| |
| #[cfg(any(feature = "std", feature = "alloc"))] |
| impl<'a, T: 'a> From<Vec<T>> for Managed<'a, [T]> { |
| fn from(value: Vec<T>) -> Self { |
| Managed::Owned(value.into_boxed_slice()) |
| } |
| } |
| |
| impl<'a, T: 'a + ?Sized> Deref for Managed<'a, T> { |
| type Target = T; |
| |
| fn deref(&self) -> &Self::Target { |
| match self { |
| &Managed::Borrowed(ref value) => value, |
| #[cfg(any(feature = "std", feature = "alloc"))] |
| &Managed::Owned(ref value) => value |
| } |
| } |
| } |
| |
| impl<'a, T: 'a + ?Sized> DerefMut for Managed<'a, T> { |
| fn deref_mut(&mut self) -> &mut Self::Target { |
| match self { |
| &mut Managed::Borrowed(ref mut value) => value, |
| #[cfg(any(feature = "std", feature = "alloc"))] |
| &mut Managed::Owned(ref mut value) => value |
| } |
| } |
| } |