1 // Copyright 2013-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! This module implements the `Any` trait, which enables dynamic typing
12 //! of any `'static` type through runtime reflection.
14 //! `Any` itself can be used to get a `TypeId`, and has more features when used
15 //! as a trait object. As `&Any` (a borrowed trait object), it has the `is` and
16 //! `downcast_ref` methods, to test if the contained value is of a given type,
17 //! and to get a reference to the inner value as a type. As `&mut Any`, there
18 //! is also the `downcast_mut` method, for getting a mutable reference to the
19 //! inner value. `Box<Any>` adds the `downcast` method, which attempts to
20 //! convert to a `Box<T>`. See the [`Box`] documentation for the full details.
22 //! Note that &Any is limited to testing whether a value is of a specified
23 //! concrete type, and cannot be used to test whether a type implements a trait.
25 //! [`Box`]: ../../std/boxed/struct.Box.html
29 //! Consider a situation where we want to log out a value passed to a function.
30 //! We know the value we're working on implements Debug, but we don't know its
31 //! concrete type. We want to give special treatment to certain types: in this
32 //! case printing out the length of String values prior to their value.
33 //! We don't know the concrete type of our value at compile time, so we need to
34 //! use runtime reflection instead.
37 //! use std::fmt::Debug;
38 //! use std::any::Any;
40 //! // Logger function for any type that implements Debug.
41 //! fn log<T: Any + Debug>(value: &T) {
42 //! let value_any = value as &Any;
44 //! // try to convert our value to a String. If successful, we want to
45 //! // output the String's length as well as its value. If not, it's a
46 //! // different type: just print it out unadorned.
47 //! match value_any.downcast_ref::<String>() {
48 //! Some(as_string) => {
49 //! println!("String ({}): {}", as_string.len(), as_string);
52 //! println!("{:?}", value);
57 //! // This function wants to log its parameter out prior to doing work with it.
58 //! fn do_work<T: Any + Debug>(value: &T) {
60 //! // ...do some other work
64 //! let my_string = "Hello World".to_string();
65 //! do_work(&my_string);
67 //! let my_i8: i8 = 100;
72 #![stable(feature = "rust1", since = "1.0.0")]
78 ///////////////////////////////////////////////////////////////////////////////
80 ///////////////////////////////////////////////////////////////////////////////
82 /// A type to emulate dynamic typing.
84 /// Most types implement `Any`. However, any type which contains a non-`'static` reference does not.
85 /// See the [module-level documentation][mod] for more details.
88 #[stable(feature = "rust1", since = "1.0.0")]
89 pub trait Any: Reflect + 'static {
90 /// Gets the `TypeId` of `self`.
95 /// #![feature(get_type_id)]
97 /// use std::any::{Any, TypeId};
99 /// fn is_string(s: &Any) -> bool {
100 /// TypeId::of::<String>() == s.get_type_id()
104 /// assert_eq!(is_string(&0), false);
105 /// assert_eq!(is_string(&"cookie monster".to_owned()), true);
108 #[unstable(feature = "get_type_id",
109 reason = "this method will likely be replaced by an associated static",
111 fn get_type_id(&self) -> TypeId;
114 #[stable(feature = "rust1", since = "1.0.0")]
115 impl<T: Reflect + 'static + ?Sized > Any for T {
116 fn get_type_id(&self) -> TypeId { TypeId::of::<T>() }
119 ///////////////////////////////////////////////////////////////////////////////
120 // Extension methods for Any trait objects.
121 ///////////////////////////////////////////////////////////////////////////////
123 #[stable(feature = "rust1", since = "1.0.0")]
124 impl fmt::Debug for Any {
125 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
130 // Ensure that the result of e.g. joining a thread can be printed and
131 // hence used with `unwrap`. May eventually no longer be needed if
132 // dispatch works with upcasting.
133 #[stable(feature = "rust1", since = "1.0.0")]
134 impl fmt::Debug for Any + Send {
135 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
141 /// Returns true if the boxed type is the same as `T`.
146 /// use std::any::Any;
148 /// fn is_string(s: &Any) {
149 /// if s.is::<String>() {
150 /// println!("It's a string!");
152 /// println!("Not a string...");
158 /// is_string(&"cookie monster".to_owned());
161 #[stable(feature = "rust1", since = "1.0.0")]
163 pub fn is<T: Any>(&self) -> bool {
164 // Get TypeId of the type this function is instantiated with
165 let t = TypeId::of::<T>();
167 // Get TypeId of the type in the trait object
168 let boxed = self.get_type_id();
170 // Compare both TypeIds on equality
174 /// Returns some reference to the boxed value if it is of type `T`, or
175 /// `None` if it isn't.
180 /// use std::any::Any;
182 /// fn print_if_string(s: &Any) {
183 /// if let Some(string) = s.downcast_ref::<String>() {
184 /// println!("It's a string({}): '{}'", string.len(), string);
186 /// println!("Not a string...");
191 /// print_if_string(&0);
192 /// print_if_string(&"cookie monster".to_owned());
195 #[stable(feature = "rust1", since = "1.0.0")]
197 pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
200 Some(&*(self as *const Any as *const T))
207 /// Returns some mutable reference to the boxed value if it is of type `T`, or
208 /// `None` if it isn't.
213 /// use std::any::Any;
215 /// fn modify_if_u32(s: &mut Any) {
216 /// if let Some(num) = s.downcast_mut::<u32>() {
222 /// let mut x = 10u32;
223 /// let mut s = "starlord".to_owned();
225 /// modify_if_u32(&mut x);
226 /// modify_if_u32(&mut s);
228 /// assert_eq!(x, 42);
229 /// assert_eq!(&s, "starlord");
232 #[stable(feature = "rust1", since = "1.0.0")]
234 pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> {
237 Some(&mut *(self as *mut Any as *mut T))
246 /// Forwards to the method defined on the type `Any`.
251 /// use std::any::Any;
253 /// fn is_string(s: &(Any + Send)) {
254 /// if s.is::<String>() {
255 /// println!("It's a string!");
257 /// println!("Not a string...");
263 /// is_string(&"cookie monster".to_owned());
266 #[stable(feature = "rust1", since = "1.0.0")]
268 pub fn is<T: Any>(&self) -> bool {
272 /// Forwards to the method defined on the type `Any`.
277 /// use std::any::Any;
279 /// fn print_if_string(s: &(Any + Send)) {
280 /// if let Some(string) = s.downcast_ref::<String>() {
281 /// println!("It's a string({}): '{}'", string.len(), string);
283 /// println!("Not a string...");
288 /// print_if_string(&0);
289 /// print_if_string(&"cookie monster".to_owned());
292 #[stable(feature = "rust1", since = "1.0.0")]
294 pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
295 Any::downcast_ref::<T>(self)
298 /// Forwards to the method defined on the type `Any`.
303 /// use std::any::Any;
305 /// fn modify_if_u32(s: &mut (Any+ Send)) {
306 /// if let Some(num) = s.downcast_mut::<u32>() {
312 /// let mut x = 10u32;
313 /// let mut s = "starlord".to_owned();
315 /// modify_if_u32(&mut x);
316 /// modify_if_u32(&mut s);
318 /// assert_eq!(x, 42);
319 /// assert_eq!(&s, "starlord");
322 #[stable(feature = "rust1", since = "1.0.0")]
324 pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> {
325 Any::downcast_mut::<T>(self)
330 ///////////////////////////////////////////////////////////////////////////////
331 // TypeID and its methods
332 ///////////////////////////////////////////////////////////////////////////////
334 /// A `TypeId` represents a globally unique identifier for a type.
336 /// Each `TypeId` is an opaque object which does not allow inspection of what's
337 /// inside but does allow basic operations such as cloning, comparison,
338 /// printing, and showing.
340 /// A `TypeId` is currently only available for types which ascribe to `'static`,
341 /// but this limitation may be removed in the future.
342 #[derive(Clone, Copy, PartialEq, Eq, Debug, Hash)]
343 #[stable(feature = "rust1", since = "1.0.0")]
349 /// Returns the `TypeId` of the type this generic function has been
350 /// instantiated with.
355 /// #![feature(get_type_id)]
357 /// use std::any::{Any, TypeId};
359 /// fn is_string(s: &Any) -> bool {
360 /// TypeId::of::<String>() == s.get_type_id()
364 /// assert_eq!(is_string(&0), false);
365 /// assert_eq!(is_string(&"cookie monster".to_owned()), true);
368 #[stable(feature = "rust1", since = "1.0.0")]
369 pub fn of<T: ?Sized + Reflect + 'static>() -> TypeId {
371 t: unsafe { intrinsics::type_id::<T>() },