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//! This module implements the `Any` trait, which enables dynamic typing
//! of any `'static` type through runtime reflection.
//!
//! `Any` itself can be used to get a `TypeId`, and has more features when used
//! as a trait object. As `&dyn Any` (a borrowed trait object), it has the `is`
//! and `downcast_ref` methods, to test if the contained value is of a given type,
//! and to get a reference to the inner value as a type. As `&mut dyn Any`, there
//! is also the `downcast_mut` method, for getting a mutable reference to the
//! inner value. `Box<dyn Any>` adds the `downcast` method, which attempts to
//! convert to a `Box<T>`. See the [`Box`] documentation for the full details.
//!
//! Note that `&dyn Any` is limited to testing whether a value is of a specified
//! concrete type, and cannot be used to test whether a type implements a trait.
//!
//! [`Box`]: ../../std/boxed/struct.Box.html
//!
//! # Examples
//!
//! Consider a situation where we want to log out a value passed to a function.
//! We know the value we're working on implements Debug, but we don't know its
//! concrete type. We want to give special treatment to certain types: in this
//! case printing out the length of String values prior to their value.
//! We don't know the concrete type of our value at compile time, so we need to
//! use runtime reflection instead.
//!
//! ```rust
//! use std::fmt::Debug;
//! use std::any::Any;
//!
//! // Logger function for any type that implements Debug.
//! fn log<T: Any + Debug>(value: &T) {
//! let value_any = value as &dyn Any;
//!
//! // Try to convert our value to a `String`. If successful, we want to
//! // output the String`'s length as well as its value. If not, it's a
//! // different type: just print it out unadorned.
//! match value_any.downcast_ref::<String>() {
//! Some(as_string) => {
//! println!("String ({}): {}", as_string.len(), as_string);
//! }
//! None => {
//! println!("{:?}", value);
//! }
//! }
//! }
//!
//! // This function wants to log its parameter out prior to doing work with it.
//! fn do_work<T: Any + Debug>(value: &T) {
//! log(value);
//! // ...do some other work
//! }
//!
//! fn main() {
//! let my_string = "Hello World".to_string();
//! do_work(&my_string);
//!
//! let my_i8: i8 = 100;
//! do_work(&my_i8);
//! }
//! ```
#![stable(feature = "rust1", since = "1.0.0")]
use crate::fmt;
use crate::intrinsics;
///////////////////////////////////////////////////////////////////////////////
// Any trait
///////////////////////////////////////////////////////////////////////////////
/// A type to emulate dynamic typing.
///
/// Most types implement `Any`. However, any type which contains a non-`'static` reference does not.
/// See the [module-level documentation][mod] for more details.
///
/// [mod]: index.html
#[stable(feature = "rust1", since = "1.0.0")]
pub trait Any: 'static {
/// Gets the `TypeId` of `self`.
///
/// # Examples
///
/// ```
/// use std::any::{Any, TypeId};
///
/// fn is_string(s: &dyn Any) -> bool {
/// TypeId::of::<String>() == s.type_id()
/// }
///
/// assert_eq!(is_string(&0), false);
/// assert_eq!(is_string(&"cookie monster".to_string()), true);
/// ```
#[stable(feature = "get_type_id", since = "1.34.0")]
fn type_id(&self) -> TypeId;
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: 'static + ?Sized > Any for T {
fn type_id(&self) -> TypeId { TypeId::of::<T>() }
}
///////////////////////////////////////////////////////////////////////////////
// Extension methods for Any trait objects.
///////////////////////////////////////////////////////////////////////////////
#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Debug for dyn Any {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.pad("Any")
}
}
// Ensure that the result of e.g., joining a thread can be printed and
// hence used with `unwrap`. May eventually no longer be needed if
// dispatch works with upcasting.
#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Debug for dyn Any + Send {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.pad("Any")
}
}
#[stable(feature = "any_send_sync_methods", since = "1.28.0")]
impl fmt::Debug for dyn Any + Send + Sync {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.pad("Any")
}
}
impl dyn Any {
/// Returns `true` if the boxed type is the same as `T`.
///
/// # Examples
///
/// ```
/// use std::any::Any;
///
/// fn is_string(s: &dyn Any) {
/// if s.is::<String>() {
/// println!("It's a string!");
/// } else {
/// println!("Not a string...");
/// }
/// }
///
/// is_string(&0);
/// is_string(&"cookie monster".to_string());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn is<T: Any>(&self) -> bool {
// Get `TypeId` of the type this function is instantiated with.
let t = TypeId::of::<T>();
// Get `TypeId` of the type in the trait object.
let concrete = self.type_id();
// Compare both `TypeId`s on equality.
t == concrete
}
/// Returns some reference to the boxed value if it is of type `T`, or
/// `None` if it isn't.
///
/// # Examples
///
/// ```
/// use std::any::Any;
///
/// fn print_if_string(s: &dyn Any) {
/// if let Some(string) = s.downcast_ref::<String>() {
/// println!("It's a string({}): '{}'", string.len(), string);
/// } else {
/// println!("Not a string...");
/// }
/// }
///
/// print_if_string(&0);
/// print_if_string(&"cookie monster".to_string());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
if self.is::<T>() {
unsafe {
Some(&*(self as *const dyn Any as *const T))
}
} else {
None
}
}
/// Returns some mutable reference to the boxed value if it is of type `T`, or
/// `None` if it isn't.
///
/// # Examples
///
/// ```
/// use std::any::Any;
///
/// fn modify_if_u32(s: &mut dyn Any) {
/// if let Some(num) = s.downcast_mut::<u32>() {
/// *num = 42;
/// }
/// }
///
/// let mut x = 10u32;
/// let mut s = "starlord".to_string();
///
/// modify_if_u32(&mut x);
/// modify_if_u32(&mut s);
///
/// assert_eq!(x, 42);
/// assert_eq!(&s, "starlord");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> {
if self.is::<T>() {
unsafe {
Some(&mut *(self as *mut dyn Any as *mut T))
}
} else {
None
}
}
}
impl dyn Any+Send {
/// Forwards to the method defined on the type `Any`.
///
/// # Examples
///
/// ```
/// use std::any::Any;
///
/// fn is_string(s: &(dyn Any + Send)) {
/// if s.is::<String>() {
/// println!("It's a string!");
/// } else {
/// println!("Not a string...");
/// }
/// }
///
/// is_string(&0);
/// is_string(&"cookie monster".to_string());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn is<T: Any>(&self) -> bool {
Any::is::<T>(self)
}
/// Forwards to the method defined on the type `Any`.
///
/// # Examples
///
/// ```
/// use std::any::Any;
///
/// fn print_if_string(s: &(dyn Any + Send)) {
/// if let Some(string) = s.downcast_ref::<String>() {
/// println!("It's a string({}): '{}'", string.len(), string);
/// } else {
/// println!("Not a string...");
/// }
/// }
///
/// print_if_string(&0);
/// print_if_string(&"cookie monster".to_string());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
Any::downcast_ref::<T>(self)
}
/// Forwards to the method defined on the type `Any`.
///
/// # Examples
///
/// ```
/// use std::any::Any;
///
/// fn modify_if_u32(s: &mut (dyn Any + Send)) {
/// if let Some(num) = s.downcast_mut::<u32>() {
/// *num = 42;
/// }
/// }
///
/// let mut x = 10u32;
/// let mut s = "starlord".to_string();
///
/// modify_if_u32(&mut x);
/// modify_if_u32(&mut s);
///
/// assert_eq!(x, 42);
/// assert_eq!(&s, "starlord");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> {
Any::downcast_mut::<T>(self)
}
}
impl dyn Any+Send+Sync {
/// Forwards to the method defined on the type `Any`.
///
/// # Examples
///
/// ```
/// use std::any::Any;
///
/// fn is_string(s: &(dyn Any + Send + Sync)) {
/// if s.is::<String>() {
/// println!("It's a string!");
/// } else {
/// println!("Not a string...");
/// }
/// }
///
/// is_string(&0);
/// is_string(&"cookie monster".to_string());
/// ```
#[stable(feature = "any_send_sync_methods", since = "1.28.0")]
#[inline]
pub fn is<T: Any>(&self) -> bool {
Any::is::<T>(self)
}
/// Forwards to the method defined on the type `Any`.
///
/// # Examples
///
/// ```
/// use std::any::Any;
///
/// fn print_if_string(s: &(dyn Any + Send + Sync)) {
/// if let Some(string) = s.downcast_ref::<String>() {
/// println!("It's a string({}): '{}'", string.len(), string);
/// } else {
/// println!("Not a string...");
/// }
/// }
///
/// print_if_string(&0);
/// print_if_string(&"cookie monster".to_string());
/// ```
#[stable(feature = "any_send_sync_methods", since = "1.28.0")]
#[inline]
pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
Any::downcast_ref::<T>(self)
}
/// Forwards to the method defined on the type `Any`.
///
/// # Examples
///
/// ```
/// use std::any::Any;
///
/// fn modify_if_u32(s: &mut (dyn Any + Send + Sync)) {
/// if let Some(num) = s.downcast_mut::<u32>() {
/// *num = 42;
/// }
/// }
///
/// let mut x = 10u32;
/// let mut s = "starlord".to_string();
///
/// modify_if_u32(&mut x);
/// modify_if_u32(&mut s);
///
/// assert_eq!(x, 42);
/// assert_eq!(&s, "starlord");
/// ```
#[stable(feature = "any_send_sync_methods", since = "1.28.0")]
#[inline]
pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> {
Any::downcast_mut::<T>(self)
}
}
///////////////////////////////////////////////////////////////////////////////
// TypeID and its methods
///////////////////////////////////////////////////////////////////////////////
/// A `TypeId` represents a globally unique identifier for a type.
///
/// Each `TypeId` is an opaque object which does not allow inspection of what's
/// inside but does allow basic operations such as cloning, comparison,
/// printing, and showing.
///
/// A `TypeId` is currently only available for types which ascribe to `'static`,
/// but this limitation may be removed in the future.
///
/// While `TypeId` implements `Hash`, `PartialOrd`, and `Ord`, it is worth
/// noting that the hashes and ordering will vary between Rust releases. Beware
/// of relying on them inside of your code!
#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct TypeId {
t: u64,
}
impl TypeId {
/// Returns the `TypeId` of the type this generic function has been
/// instantiated with.
///
/// # Examples
///
/// ```
/// use std::any::{Any, TypeId};
///
/// fn is_string<T: ?Sized + Any>(_s: &T) -> bool {
/// TypeId::of::<String>() == TypeId::of::<T>()
/// }
///
/// assert_eq!(is_string(&0), false);
/// assert_eq!(is_string(&"cookie monster".to_string()), true);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature="const_type_id")]
pub const fn of<T: ?Sized + 'static>() -> TypeId {
TypeId {
t: unsafe { intrinsics::type_id::<T>() },
}
}
}
/// Returns the name of a type as a string slice.
///
/// # Note
///
/// This is intended for diagnostic use. The exact contents and format of the
/// string are not specified, other than being a best-effort description of the
/// type. For example, `type_name::<Option<String>>()` could return the
/// `"Option<String>"` or `"std::option::Option<std::string::String>"`, but not
/// `"foobar"`. In addition, the output may change between versions of the
/// compiler.
///
/// The type name should not be considered a unique identifier of a type;
/// multiple types may share the same type name.
///
/// The current implementation uses the same infrastructure as compiler
/// diagnostics and debuginfo, but this is not guaranteed.
#[stable(feature = "type_name", since = "1.38.0")]
#[rustc_const_unstable(feature = "const_type_name")]
pub const fn type_name<T: ?Sized>() -> &'static str {
intrinsics::type_name::<T>()
}
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