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")]
77 ///////////////////////////////////////////////////////////////////////////////
79 ///////////////////////////////////////////////////////////////////////////////
81 /// A type to emulate dynamic typing.
83 /// Most types implement `Any`. However, any type which contains a non-`'static` reference does not.
84 /// See the [module-level documentation][mod] for more details.
87 #[stable(feature = "rust1", since = "1.0.0")]
88 pub trait Any
: '
static {
89 /// Gets the `TypeId` of `self`.
94 /// #![feature(get_type_id)]
96 /// use std::any::{Any, TypeId};
98 /// fn is_string(s: &Any) -> bool {
99 /// TypeId::of::<String>() == s.get_type_id()
103 /// assert_eq!(is_string(&0), false);
104 /// assert_eq!(is_string(&"cookie monster".to_string()), true);
107 #[unstable(feature = "get_type_id",
108 reason
= "this method will likely be replaced by an associated static",
110 fn get_type_id(&self) -> TypeId
;
113 #[stable(feature = "rust1", since = "1.0.0")]
114 impl<T
: '
static + ?Sized
> Any
for T
{
115 fn get_type_id(&self) -> TypeId { TypeId::of::<T>() }
118 ///////////////////////////////////////////////////////////////////////////////
119 // Extension methods for Any trait objects.
120 ///////////////////////////////////////////////////////////////////////////////
122 #[stable(feature = "rust1", since = "1.0.0")]
123 impl fmt
::Debug
for Any
{
124 fn fmt(&self, f
: &mut fmt
::Formatter
) -> fmt
::Result
{
129 // Ensure that the result of e.g. joining a thread can be printed and
130 // hence used with `unwrap`. May eventually no longer be needed if
131 // dispatch works with upcasting.
132 #[stable(feature = "rust1", since = "1.0.0")]
133 impl fmt
::Debug
for Any
+ Send
{
134 fn fmt(&self, f
: &mut fmt
::Formatter
) -> fmt
::Result
{
140 /// Returns `true` if the boxed type is the same as `T`.
145 /// use std::any::Any;
147 /// fn is_string(s: &Any) {
148 /// if s.is::<String>() {
149 /// println!("It's a string!");
151 /// println!("Not a string...");
157 /// is_string(&"cookie monster".to_string());
160 #[stable(feature = "rust1", since = "1.0.0")]
162 pub fn is
<T
: Any
>(&self) -> bool
{
163 // Get TypeId of the type this function is instantiated with
164 let t
= TypeId
::of
::<T
>();
166 // Get TypeId of the type in the trait object
167 let boxed
= self.get_type_id();
169 // Compare both TypeIds on equality
173 /// Returns some reference to the boxed value if it is of type `T`, or
174 /// `None` if it isn't.
179 /// use std::any::Any;
181 /// fn print_if_string(s: &Any) {
182 /// if let Some(string) = s.downcast_ref::<String>() {
183 /// println!("It's a string({}): '{}'", string.len(), string);
185 /// println!("Not a string...");
190 /// print_if_string(&0);
191 /// print_if_string(&"cookie monster".to_string());
194 #[stable(feature = "rust1", since = "1.0.0")]
196 pub fn downcast_ref
<T
: Any
>(&self) -> Option
<&T
> {
199 Some(&*(self as *const Any
as *const T
))
206 /// Returns some mutable reference to the boxed value if it is of type `T`, or
207 /// `None` if it isn't.
212 /// use std::any::Any;
214 /// fn modify_if_u32(s: &mut Any) {
215 /// if let Some(num) = s.downcast_mut::<u32>() {
221 /// let mut x = 10u32;
222 /// let mut s = "starlord".to_string();
224 /// modify_if_u32(&mut x);
225 /// modify_if_u32(&mut s);
227 /// assert_eq!(x, 42);
228 /// assert_eq!(&s, "starlord");
231 #[stable(feature = "rust1", since = "1.0.0")]
233 pub fn downcast_mut
<T
: Any
>(&mut self) -> Option
<&mut T
> {
236 Some(&mut *(self as *mut Any
as *mut T
))
245 /// Forwards to the method defined on the type `Any`.
250 /// use std::any::Any;
252 /// fn is_string(s: &(Any + Send)) {
253 /// if s.is::<String>() {
254 /// println!("It's a string!");
256 /// println!("Not a string...");
262 /// is_string(&"cookie monster".to_string());
265 #[stable(feature = "rust1", since = "1.0.0")]
267 pub fn is
<T
: Any
>(&self) -> bool
{
271 /// Forwards to the method defined on the type `Any`.
276 /// use std::any::Any;
278 /// fn print_if_string(s: &(Any + Send)) {
279 /// if let Some(string) = s.downcast_ref::<String>() {
280 /// println!("It's a string({}): '{}'", string.len(), string);
282 /// println!("Not a string...");
287 /// print_if_string(&0);
288 /// print_if_string(&"cookie monster".to_string());
291 #[stable(feature = "rust1", since = "1.0.0")]
293 pub fn downcast_ref
<T
: Any
>(&self) -> Option
<&T
> {
294 Any
::downcast_ref
::<T
>(self)
297 /// Forwards to the method defined on the type `Any`.
302 /// use std::any::Any;
304 /// fn modify_if_u32(s: &mut (Any+ Send)) {
305 /// if let Some(num) = s.downcast_mut::<u32>() {
311 /// let mut x = 10u32;
312 /// let mut s = "starlord".to_string();
314 /// modify_if_u32(&mut x);
315 /// modify_if_u32(&mut s);
317 /// assert_eq!(x, 42);
318 /// assert_eq!(&s, "starlord");
321 #[stable(feature = "rust1", since = "1.0.0")]
323 pub fn downcast_mut
<T
: Any
>(&mut self) -> Option
<&mut T
> {
324 Any
::downcast_mut
::<T
>(self)
329 ///////////////////////////////////////////////////////////////////////////////
330 // TypeID and its methods
331 ///////////////////////////////////////////////////////////////////////////////
333 /// A `TypeId` represents a globally unique identifier for a type.
335 /// Each `TypeId` is an opaque object which does not allow inspection of what's
336 /// inside but does allow basic operations such as cloning, comparison,
337 /// printing, and showing.
339 /// A `TypeId` is currently only available for types which ascribe to `'static`,
340 /// but this limitation may be removed in the future.
342 /// While `TypeId` implements `Hash`, `PartialOrd`, and `Ord`, it is worth
343 /// noting that the hashes and ordering will vary between Rust releases. Beware
344 /// of relying on them outside of your code!
345 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
346 #[stable(feature = "rust1", since = "1.0.0")]
352 /// Returns the `TypeId` of the type this generic function has been
353 /// instantiated with.
358 /// use std::any::{Any, TypeId};
360 /// fn is_string<T: ?Sized + Any>(_s: &T) -> bool {
361 /// TypeId::of::<String>() == TypeId::of::<T>()
365 /// assert_eq!(is_string(&0), false);
366 /// assert_eq!(is_string(&"cookie monster".to_string()), true);
369 #[stable(feature = "rust1", since = "1.0.0")]
370 pub fn of
<T
: ?Sized
+ '
static>() -> TypeId
{
372 t
: unsafe { intrinsics::type_id::<T>() }
,