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//! A more compact, user friendly clone-on-write smart pointer. //! //! ``` //! use dairy::Cow; //! let borrowed: Cow<str> = Cow::borrowed("Hello World!"); //! let owned: Cow<str> = Cow::owned(String::from("Hello World!")); //! ``` //! //! [`dairy::Cow`][Cow] is an improved version of the standard library //! [`std::borrow::Cow`]. Depending on the platform and type this crate provides //! a better underlying implementation which will be more compact. This crate //! currently supports the following types: [`str`], [`[T]`][slice], [`CStr`], //! [`OsStr`], and [`Path`]. //! //! [`dairy::Cow`][Cow] is also able to provide many more [`From`] //! implementations; some which are not possible for the standard library to //! provide due to the `alloc`, `std` split. For example `Cow<Path>` now has //! the useful `From<&str>` implementation. //! //! ### Underlying implementation //! //! - On 64-bit platforms the *compact* implementation of [`Cow`] is two words //! wide, storing the length, capacity, and the ownership tag in the same //! word. //! - On 32-bit platforms the *compact* implementation of [`Cow`] is three words //! wide, storing the capacity and the ownership tag in the same word. //! - The **default** implementation simply uses the the standard library //! implementation which is four words wide. This is typically required in //! cases where the standard library does not provide an `.into_raw_parts()` //! or equivalent method for the owned version of types. //! //! The following table documents how `Cow<T>` is implemented for each type on //! depending on the platform. //! //! | `Cow<T>` | Unix/WASI | Other | //! | ------------ | --------- | -------------- | //! | `Cow<str>` | *compact* | *compact* | //! | `Cow<[T]>` | *compact* | *compact* | //! | `Cow<CStr>` | *compact* | *compact* | //! | `Cow<OsStr>` | *compact* | **default** | //! | `Cow<Path>` | *compact* | **default** | #![no_std] #![warn(unsafe_op_in_unsafe_fn)] extern crate alloc; #[cfg(feature = "std")] extern crate std; mod as_ref; mod cmp; mod extend; mod from; mod from_iter; mod from_str; mod imp; mod serde; mod to_boxed; use core::borrow::Borrow; use core::fmt; use core::hash::{Hash, Hasher}; use core::marker::Unpin; use core::ops::Deref; use alloc::boxed::Box; #[cfg(feature = "std")] use std::{ ffi::{CStr, OsStr}, path::Path, }; use crate::imp::Cow as _; pub use crate::imp::Dairy; pub use crate::to_boxed::ToBoxed; /// Convenient type alias for a clone-on-write [`str`]. pub type String<'a> = Cow<'a, str>; /// Convenient type alias for a clone-on-write [`[T]`][slice]. pub type Vec<'a, T> = Cow<'a, [T]>; /// Convenient type alias for a clone-on-write [`CStr`]. #[cfg(feature = "std")] pub type CString<'a> = Cow<'a, CStr>; /// Convenient type alias for a clone-on-write [`OsStr`]. #[cfg(feature = "std")] pub type OsString<'a> = Cow<'a, OsStr>; /// Convenient type alias for a clone-on-write [`Path`]. #[cfg(feature = "std")] pub type PathBuf<'a> = Cow<'a, Path>; /// A clone-on-write smart pointer. /// /// The type `Cow` is a smart pointer providing clone-on-write functionality: it /// can enclose and provide immutable access to borrowed data, and clone the /// data lazily when mutation or ownership is required. /// /// `Cow` implements [`Deref`], which means that you can call non-mutating /// methods directly on the data it encloses. pub struct Cow<'a, T> where T: ?Sized + Dairy<'a>, { inner: T::Cow, } impl<'a, T> Cow<'a, T> where T: ?Sized + Dairy<'a>, { /// Construct from borrowed data. /// /// # Examples /// /// ``` /// use dairy::Cow; /// let cow: Cow<str> = Cow::borrowed("moo"); /// ``` #[inline] pub fn borrowed(b: &'a T) -> Self { Self { inner: T::Cow::borrowed(b), } } /// Construct from owned data. /// /// # Examples /// /// ``` /// use dairy::Cow; /// let cow: Cow<str> = Cow::owned(String::from("moo")); /// ``` #[inline] pub fn owned(o: T::Owned) -> Self { Self { inner: T::Cow::owned(o), } } /// Returns true if the data is borrowed. /// /// # Examples /// /// ``` /// use dairy::Cow; /// /// let cow: Cow<str> = Cow::borrowed("moo"); /// assert!(cow.is_borrowed()); /// /// let cow: Cow<str> = Cow::owned(String::from("...moo?")); /// assert!(!cow.is_borrowed()); /// ``` #[inline] pub fn is_borrowed(&self) -> bool { self.inner.is_borrowed() } /// Returns true if the data is owned. /// /// # Examples /// /// ``` /// use dairy::Cow; /// /// let cow: Cow<str> = Cow::owned(String::from("moo")); /// assert!(cow.is_owned()); /// /// let cow: Cow<str> = Cow::borrowed("...moo?"); /// assert!(!cow.is_owned()); /// ``` #[inline] pub fn is_owned(&self) -> bool { self.inner.is_owned() } #[inline] fn make_ref(&self) -> &T { self.inner.make_ref() } /// Converts into owned data. /// /// Clones the data if it is not already owned. /// /// # Examples /// /// Calling `.into_owned()` on a borrowed `Cow` clones the underlying data. /// /// ``` /// use dairy::Cow; /// /// let cow = Cow::borrowed("Moo!"); /// assert_eq!(cow.into_owned(), String::from("Moo!")); /// ``` /// /// Calling `.into_owned()` on an owned `Cow` is a noop. /// /// ``` /// use dairy::Cow; /// /// let cow: Cow<str> = Cow::owned(String::from("Moo!")); /// assert_eq!(cow.into_owned(), String::from("Moo!")); /// ``` #[inline] pub fn into_owned(self) -> T::Owned { self.inner.into_owned() } /// Converts into boxed data. /// /// Clones the data if it is not already owned. /// /// # Examples /// /// Calling `.into_boxed()` on a borrowed `Cow` clones the underlying data. /// /// ``` /// use dairy::Cow; /// /// let cow = Cow::borrowed("Moo!"); /// assert_eq!(cow.into_boxed(), String::from("Moo!").into_boxed_str()); /// ``` /// /// Calling `.into_boxed()` on an owned `Cow` is a noop. /// /// ``` /// use dairy::Cow; /// /// let cow: Cow<str> = Cow::owned(String::from("Moo!")); /// assert_eq!(cow.into_boxed(), String::from("Moo!").into_boxed_str()); /// ``` #[inline] pub fn into_boxed(self) -> Box<T> where T: ToBoxed, { T::to_boxed(self.into_owned()) } /// Applies the given function to the owned data. /// /// Clones the data if it is not already owned. This is useful because the /// compact implementation is not able to provide a `.to_mut()` method like /// the standard library. This function allows you to modify the `Cow` /// without [moving] it. /// /// # Examples /// /// ``` /// use dairy::Cow; /// /// let mut cow = Cow::borrowed("Moo!"); /// cow.apply(|s| s.make_ascii_uppercase()); /// assert_eq!(cow, "MOO!"); /// ``` /// /// [moving]: https://doc.rust-lang.org/book/ch04-01-what-is-ownership.html?#ways-variables-and-data-interact-move #[inline] pub fn apply<F>(&mut self, f: F) where F: FnOnce(&mut T::Owned), { self.inner.apply(f) } } impl<'a, T> Deref for Cow<'a, T> where T: ?Sized + Dairy<'a>, { type Target = T; #[inline] fn deref(&self) -> &T { self.make_ref() } } impl<'a, T> Borrow<T> for Cow<'a, T> where T: ?Sized + Dairy<'a>, { #[inline] fn borrow(&self) -> &T { self.make_ref() } } impl<'a, T> Clone for Cow<'a, T> where T: ?Sized + Dairy<'a>, { #[inline] fn clone(&self) -> Self { Self { inner: self.inner.clone(), } } } impl<'a, T> fmt::Debug for Cow<'a, T> where T: ?Sized + Dairy<'a> + fmt::Debug, T::Owned: fmt::Debug, { #[inline] fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { fmt::Debug::fmt(&**self, f) } } impl<'a, T> fmt::Display for Cow<'a, T> where T: ?Sized + Dairy<'a> + fmt::Display, T::Owned: fmt::Display, { #[inline] fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { fmt::Display::fmt(&**self, f) } } impl<'a, T> Default for Cow<'a, T> where T: ?Sized + Dairy<'a>, T::Owned: Default, { #[inline] fn default() -> Self { Self::owned(T::Owned::default()) } } impl<'a, T> Hash for Cow<'a, T> where T: ?Sized + Dairy<'a> + Hash, { #[inline] fn hash<H: Hasher>(&self, state: &mut H) { Hash::hash(&**self, state) } } unsafe impl<'a, T> Send for Cow<'a, T> where T: ?Sized + Dairy<'a> + Sync, T::Owned: Send, { } unsafe impl<'a, T> Sync for Cow<'a, T> where T: ?Sized + Dairy<'a> + Sync, T::Owned: Sync, { } impl<'a, T> Unpin for Cow<'a, T> where T: ?Sized + Dairy<'a>, T::Owned: Unpin, { }