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