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 use option
::Option
::{self, Some, None}
;
80 use marker
::{Reflect, Sized}
;
82 ///////////////////////////////////////////////////////////////////////////////
84 ///////////////////////////////////////////////////////////////////////////////
86 /// A type to emulate dynamic typing.
88 /// Every type with no non-`'static` references implements `Any`.
89 /// See the [module-level documentation][mod] for more details.
92 #[stable(feature = "rust1", since = "1.0.0")]
93 pub trait Any
: Reflect
+ '
static {
94 /// Gets the `TypeId` of `self`.
95 #[unstable(feature = "get_type_id",
96 reason
= "this method will likely be replaced by an associated static",
98 fn get_type_id(&self) -> TypeId
;
101 #[stable(feature = "rust1", since = "1.0.0")]
102 impl<T
: Reflect
+ '
static + ?Sized
> Any
for T
{
103 fn get_type_id(&self) -> TypeId { TypeId::of::<T>() }
106 ///////////////////////////////////////////////////////////////////////////////
107 // Extension methods for Any trait objects.
108 ///////////////////////////////////////////////////////////////////////////////
110 #[stable(feature = "rust1", since = "1.0.0")]
111 impl fmt
::Debug
for Any
{
112 fn fmt(&self, f
: &mut fmt
::Formatter
) -> fmt
::Result
{
117 // Ensure that the result of e.g. joining a thread can be printed and
118 // hence used with `unwrap`. May eventually no longer be needed if
119 // dispatch works with upcasting.
120 #[stable(feature = "rust1", since = "1.0.0")]
121 impl fmt
::Debug
for Any
+ Send
{
122 fn fmt(&self, f
: &mut fmt
::Formatter
) -> fmt
::Result
{
128 /// Returns true if the boxed type is the same as `T`
129 #[stable(feature = "rust1", since = "1.0.0")]
131 pub fn is
<T
: Any
>(&self) -> bool
{
132 // Get TypeId of the type this function is instantiated with
133 let t
= TypeId
::of
::<T
>();
135 // Get TypeId of the type in the trait object
136 let boxed
= self.get_type_id();
138 // Compare both TypeIds on equality
142 /// Returns some reference to the boxed value if it is of type `T`, or
143 /// `None` if it isn't.
144 #[stable(feature = "rust1", since = "1.0.0")]
146 pub fn downcast_ref
<T
: Any
>(&self) -> Option
<&T
> {
149 // Get the raw representation of the trait object
150 let to
: TraitObject
= transmute(self);
152 // Extract the data pointer
153 Some(&*(to
.data
as *const T
))
160 /// Returns some mutable reference to the boxed value if it is of type `T`, or
161 /// `None` if it isn't.
162 #[stable(feature = "rust1", since = "1.0.0")]
164 pub fn downcast_mut
<T
: Any
>(&mut self) -> Option
<&mut T
> {
167 // Get the raw representation of the trait object
168 let to
: TraitObject
= transmute(self);
170 // Extract the data pointer
171 Some(&mut *(to
.data
as *const T
as *mut T
))
180 /// Forwards to the method defined on the type `Any`.
181 #[stable(feature = "rust1", since = "1.0.0")]
183 pub fn is
<T
: Any
>(&self) -> bool
{
187 /// Forwards to the method defined on the type `Any`.
188 #[stable(feature = "rust1", since = "1.0.0")]
190 pub fn downcast_ref
<T
: Any
>(&self) -> Option
<&T
> {
191 Any
::downcast_ref
::<T
>(self)
194 /// Forwards to the method defined on the type `Any`.
195 #[stable(feature = "rust1", since = "1.0.0")]
197 pub fn downcast_mut
<T
: Any
>(&mut self) -> Option
<&mut T
> {
198 Any
::downcast_mut
::<T
>(self)
203 ///////////////////////////////////////////////////////////////////////////////
204 // TypeID and its methods
205 ///////////////////////////////////////////////////////////////////////////////
207 /// A `TypeId` represents a globally unique identifier for a type.
209 /// Each `TypeId` is an opaque object which does not allow inspection of what's
210 /// inside but does allow basic operations such as cloning, comparison,
211 /// printing, and showing.
213 /// A `TypeId` is currently only available for types which ascribe to `'static`,
214 /// but this limitation may be removed in the future.
215 #[derive(Clone, Copy, PartialEq, Eq, Debug, Hash)]
216 #[stable(feature = "rust1", since = "1.0.0")]
222 /// Returns the `TypeId` of the type this generic function has been
223 /// instantiated with
224 #[stable(feature = "rust1", since = "1.0.0")]
225 pub fn of
<T
: ?Sized
+ Reflect
+ '
static>() -> TypeId
{
227 t
: unsafe { intrinsics::type_id::<T>() }
,