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Convert docs clean up.

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This commit is contained in:
Dylan Maccora 2017-04-01 15:35:03 +11:00
parent 7846dbe0c8
commit 7897e168bd
1 changed files with 114 additions and 31 deletions
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145
src/libcore/convert.rs
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@ -17,8 +17,8 @@
//! Like many traits, these are often used as bounds for generic functions, to
//! support arguments of multiple types.
//!
//! - Impl the `As*` traits for reference-to-reference conversions
//! - Impl the [`Into`] trait when you want to consume the value in the conversion
//! - Implement the `As*` traits for reference-to-reference conversions
//! - Implement the [`Into`] trait when you want to consume the value in the conversion
//! - The [`From`] trait is the most flexible, useful for value _and_ reference conversions
//! - The [`TryFrom`] and [`TryInto`] traits behave like [`From`] and [`Into`], but allow for the
//! conversion to fail
@ -29,7 +29,7 @@
//! equivalent [`Into`] or [`TryInto`] implementations for free, thanks to a blanket implementation
//! in the standard library.
//!
//! # Generic impl
//! # Generic Implementations
//!
//! - [`AsRef`] and [`AsMut`] auto-dereference if the inner type is a reference
//! - [`From`]`<U> for T` implies [`Into`]`<T> for U`
@ -50,10 +50,20 @@
use str::FromStr;
/// A cheap, reference-to-reference conversion.
/// A cheap reference-to-reference conversion. Used to convert a value to a reference value
/// within generic code.
///
/// `AsRef` is very similar to, but different than, [`Borrow`]. See
/// [the book][book] for more.
/// `AsRef` is very similar to, but serves a slightly different purpose than, [`Borrow`].
///
/// `AsRef` is to be used when wishing to convert to a reference of another type.
/// `Borrow` is more related to the notion of taking the reference. It is useful when wishing to abstract
/// over the type of reference (`&T`, `&mut T`) or allow both the referenced and owned type to be treated in the same manner.
/// The key difference between the two traits is the intention:
///
/// - Use `AsRef` when goal is to simply convert into a reference
/// - Use `Borrow` when goal is related to writing code that is agnostic to the type of borrow and if is reference or value
///
/// See [the book][book] for a more detailed comparison.
///
/// [book]: ../../book/borrow-and-asref.html
/// [`Borrow`]: ../../std/borrow/trait.Borrow.html
@ -64,7 +74,23 @@ use str::FromStr;
/// [`Option<T>`]: ../../std/option/enum.Option.html
/// [`Result<T, E>`]: ../../std/result/enum.Result.html
///
/// # Generic Implementations
///
/// - `AsRef` auto-dereferences if the inner type is a reference or a mutable
/// reference (e.g.: `foo.as_ref()` will work the same if `foo` has type `&mut Foo` or `&&mut Foo`)
///
/// # Examples
/// An example implementation of the trait is [`Path`].
///
/// [`Path`]: ../../std/struct.Path.html
///
/// ```
/// impl AsRef<Path> for str {
/// fn as_ref(&self) -> &Path {
/// Path::new(self)
/// }
/// }
/// ```
///
/// Both [`String`] and `&str` implement `AsRef<str>`:
///
@ -82,11 +108,6 @@ use str::FromStr;
/// is_hello(s);
/// ```
///
/// # Generic Impls
///
/// - `AsRef` auto-dereferences if the inner type is a reference or a mutable
/// reference (e.g.: `foo.as_ref()` will work the same if `foo` has type `&mut Foo` or `&&mut Foo`)
///
#[stable(feature = "rust1", since = "1.0.0")]
pub trait AsRef<T: ?Sized> {
/// Performs the conversion.
@ -96,12 +117,19 @@ pub trait AsRef<T: ?Sized> {
/// A cheap, mutable reference-to-mutable reference conversion.
///
/// This trait is similar to `AsRef` but used for converting mutable references.
///
/// **Note: this trait must not fail**. If the conversion can fail, use a dedicated method which
/// returns an [`Option<T>`] or a [`Result<T, E>`].
///
/// [`Option<T>`]: ../../std/option/enum.Option.html
/// [`Result<T, E>`]: ../../std/result/enum.Result.html
///
/// # Generic Implementations
///
/// - `AsMut` auto-dereferences if the inner type is a reference or a mutable
/// reference (e.g.: `foo.as_ref()` will work the same if `foo` has type `&mut Foo` or `&&mut Foo`)
///
/// # Examples
///
/// [`Box<T>`] implements `AsMut<T>`:
@ -118,10 +146,13 @@ pub trait AsRef<T: ?Sized> {
/// assert_eq!(*boxed_num, 1);
/// ```
///
/// # Generic Impls
/// Implementing `AsMut`:
///
/// - `AsMut` auto-dereferences if the inner type is a reference or a mutable
/// reference (e.g.: `foo.as_ref()` will work the same if `foo` has type `&mut Foo` or `&&mut Foo`)
/// ```
/// impl Type {
/// let a = 1;
/// }
/// ```
///
#[stable(feature = "rust1", since = "1.0.0")]
pub trait AsMut<T: ?Sized> {
@ -130,7 +161,7 @@ pub trait AsMut<T: ?Sized> {
fn as_mut(&mut self) -> &mut T;
}
/// A conversion that consumes `self`, which may or may not be expensive.
/// A conversion that consumes `self`, which may or may not be expensive. The reciprocal of [`From`][From].
///
/// **Note: this trait must not fail**. If the conversion can fail, use [`TryInto`] or a dedicated
/// method which returns an [`Option<T>`] or a [`Result<T, E>`].
@ -139,6 +170,11 @@ pub trait AsMut<T: ?Sized> {
/// the [`From`][From] trait, which offers greater flexibility and provides an equivalent `Into`
/// implementation for free, thanks to a blanket implementation in the standard library.
///
/// # Generic Implementations
///
/// - [`From<T>`][From]` for U` implies `Into<U> for T`
/// - [`into`] is reflexive, which means that `Into<T> for T` is implemented
///
/// # Examples
///
/// [`String`] implements `Into<Vec<u8>>`:
@ -153,11 +189,6 @@ pub trait AsMut<T: ?Sized> {
/// is_hello(s);
/// ```
///
/// # Generic Impls
///
/// - [`From<T>`][From]` for U` implies `Into<U> for T`
/// - [`into`] is reflexive, which means that `Into<T> for T` is implemented
///
/// [`TryInto`]: trait.TryInto.html
/// [`Option<T>`]: ../../std/option/enum.Option.html
/// [`Result<T, E>`]: ../../std/result/enum.Result.html
@ -171,11 +202,24 @@ pub trait Into<T>: Sized {
fn into(self) -> T;
}
/// Construct `Self` via a conversion.
/// Simple and safe type conversions in to `Self`. It is the reciprocal of `Into`.
///
/// This trait is useful when performing error handling as described by [the book][book] and is closely related to the `?` operator.
///
/// When constructing a function that is capable of failing the return type will generally be of the form `Result<T, E>`.
/// The `From` trait allows for simplification of error handling by providing a means of returning a single error type that encapsulates
/// numerous possible erroneous situations.
/// This trait is not limited to error handling, rather the general case for this trait would be in any type conversions to have an
/// explicit definition of how they are performed.
///
/// **Note: this trait must not fail**. If the conversion can fail, use [`TryFrom`] or a dedicated
/// method which returns an [`Option<T>`] or a [`Result<T, E>`].
///
/// # Generic Implementations
///
/// - `From<T> for U` implies [`Into<U>`]` for T`
/// - [`from`] is reflexive, which means that `From<T> for T` is implemented
///
/// # Examples
///
/// [`String`] implements `From<&str>`:
@ -186,10 +230,34 @@ pub trait Into<T>: Sized {
///
/// assert_eq!(string, other_string);
/// ```
/// # Generic impls
///
/// - `From<T> for U` implies [`Into<U>`]` for T`
/// - [`from`] is reflexive, which means that `From<T> for T` is implemented
/// An example usage for error handling:
///
/// ```
/// enum CliError {
/// IoError(io::Error),
/// ParseError(num::ParseIntError),
/// }
///
/// impl From<io::Error> for MyError {
/// fn from(error: io::Error) -> Self {
/// CliError::IoError(error)
/// }
/// }
///
/// impl From<num::ParseIntError> for MyError {
/// fn from(error: io::Error) -> Self {
/// CliError::ParseError(error)
/// }
/// }
///
/// fn open_and_parse_file(file_name: &str) -> Result<i32, MyError> {
/// let file = std::fs::File::open("test")?;
/// let mut contents = String::new();
/// file.read_to_string(&mut contents)?;
/// let num: i32 = contents.trim().parse()?;
/// }
/// ```
///
/// [`TryFrom`]: trait.TryFrom.html
/// [`Option<T>`]: ../../std/option/enum.Option.html
@ -197,6 +265,7 @@ pub trait Into<T>: Sized {
/// [`String`]: ../../std/string/struct.String.html
/// [`Into<U>`]: trait.Into.html
/// [`from`]: trait.From.html#tymethod.from
/// [book]: ../../book/error-handling.html#the-from-trait
#[stable(feature = "rust1", since = "1.0.0")]
pub trait From<T>: Sized {
/// Performs the conversion.
@ -236,7 +305,9 @@ pub trait TryFrom<T>: Sized {
// As lifts over &
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, T: ?Sized, U: ?Sized> AsRef<U> for &'a T where T: AsRef<U> {
impl<'a, T: ?Sized, U: ?Sized> AsRef<U> for &'a T
where T: AsRef<U>
{
fn as_ref(&self) -> &U {
<T as AsRef<U>>::as_ref(*self)
}
@ -244,7 +315,9 @@ impl<'a, T: ?Sized, U: ?Sized> AsRef<U> for &'a T where T: AsRef<U> {
// As lifts over &mut
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, T: ?Sized, U: ?Sized> AsRef<U> for &'a mut T where T: AsRef<U> {
impl<'a, T: ?Sized, U: ?Sized> AsRef<U> for &'a mut T
where T: AsRef<U>
{
fn as_ref(&self) -> &U {
<T as AsRef<U>>::as_ref(*self)
}
@ -260,7 +333,9 @@ impl<'a, T: ?Sized, U: ?Sized> AsRef<U> for &'a mut T where T: AsRef<U> {
// AsMut lifts over &mut
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, T: ?Sized, U: ?Sized> AsMut<U> for &'a mut T where T: AsMut<U> {
impl<'a, T: ?Sized, U: ?Sized> AsMut<U> for &'a mut T
where T: AsMut<U>
{
fn as_mut(&mut self) -> &mut U {
(*self).as_mut()
}
@ -276,7 +351,9 @@ impl<'a, T: ?Sized, U: ?Sized> AsMut<U> for &'a mut T where T: AsMut<U> {
// From implies Into
#[stable(feature = "rust1", since = "1.0.0")]
impl<T, U> Into<U> for T where U: From<T> {
impl<T, U> Into<U> for T
where U: From<T>
{
fn into(self) -> U {
U::from(self)
}
@ -285,13 +362,17 @@ impl<T, U> Into<U> for T where U: From<T> {
// From (and thus Into) is reflexive
#[stable(feature = "rust1", since = "1.0.0")]
impl<T> From<T> for T {
fn from(t: T) -> T { t }
fn from(t: T) -> T {
t
}
}
// TryFrom implies TryInto
#[unstable(feature = "try_from", issue = "33417")]
impl<T, U> TryInto<U> for T where U: TryFrom<T> {
impl<T, U> TryInto<U> for T
where U: TryFrom<T>
{
type Error = U::Error;
fn try_into(self) -> Result<U, U::Error> {
@ -327,7 +408,9 @@ impl AsRef<str> for str {
// FromStr implies TryFrom<&str>
#[unstable(feature = "try_from", issue = "33417")]
impl<'a, T> TryFrom<&'a str> for T where T: FromStr {
impl<'a, T> TryFrom<&'a str> for T
where T: FromStr
{
type Error = <T as FromStr>::Err;
fn try_from(s: &'a str) -> Result<T, Self::Error> {