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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.
4 //
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.
10
11 //! This module implements the `Any` trait, which enables dynamic typing
12 //! of any `'static` type through runtime reflection.
13 //!
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.
21 //!
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.
24 //!
25 //! [`Box`]: ../../std/boxed/struct.Box.html
26 //!
27 //! # Examples
28 //!
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.
35 //!
36 //! ```rust
37 //! use std::fmt::Debug;
38 //! use std::any::Any;
39 //!
40 //! // Logger function for any type that implements Debug.
41 //! fn log<T: Any + Debug>(value: &T) {
42 //! let value_any = value as &Any;
43 //!
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);
50 //! }
51 //! None => {
52 //! println!("{:?}", value);
53 //! }
54 //! }
55 //! }
56 //!
57 //! // This function wants to log its parameter out prior to doing work with it.
58 //! fn do_work<T: Any + Debug>(value: &T) {
59 //! log(value);
60 //! // ...do some other work
61 //! }
62 //!
63 //! fn main() {
64 //! let my_string = "Hello World".to_string();
65 //! do_work(&my_string);
66 //!
67 //! let my_i8: i8 = 100;
68 //! do_work(&my_i8);
69 //! }
70 //! ```
71
72 #![stable(feature = "rust1", since = "1.0.0")]
73
74 use fmt;
75 use marker::Send;
76 use mem::transmute;
77 use option::Option::{self, Some, None};
78 use raw::TraitObject;
79 use intrinsics;
80 use marker::{Reflect, Sized};
81
82 ///////////////////////////////////////////////////////////////////////////////
83 // Any trait
84 ///////////////////////////////////////////////////////////////////////////////
85
86 /// A type to emulate dynamic typing.
87 ///
88 /// Every type with no non-`'static` references implements `Any`.
89 /// See the [module-level documentation][mod] for more details.
90 ///
91 /// [mod]: index.html
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",
97 issue = "27745")]
98 fn get_type_id(&self) -> TypeId;
99 }
100
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>() }
104 }
105
106 ///////////////////////////////////////////////////////////////////////////////
107 // Extension methods for Any trait objects.
108 ///////////////////////////////////////////////////////////////////////////////
109
110 #[stable(feature = "rust1", since = "1.0.0")]
111 impl fmt::Debug for Any {
112 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
113 f.pad("Any")
114 }
115 }
116
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 {
123 f.pad("Any")
124 }
125 }
126
127 impl Any {
128 /// Returns true if the boxed type is the same as `T`
129 #[stable(feature = "rust1", since = "1.0.0")]
130 #[inline]
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>();
134
135 // Get TypeId of the type in the trait object
136 let boxed = self.get_type_id();
137
138 // Compare both TypeIds on equality
139 t == boxed
140 }
141
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")]
145 #[inline]
146 pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
147 if self.is::<T>() {
148 unsafe {
149 // Get the raw representation of the trait object
150 let to: TraitObject = transmute(self);
151
152 // Extract the data pointer
153 Some(&*(to.data as *const T))
154 }
155 } else {
156 None
157 }
158 }
159
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")]
163 #[inline]
164 pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> {
165 if self.is::<T>() {
166 unsafe {
167 // Get the raw representation of the trait object
168 let to: TraitObject = transmute(self);
169
170 // Extract the data pointer
171 Some(&mut *(to.data as *const T as *mut T))
172 }
173 } else {
174 None
175 }
176 }
177 }
178
179 impl Any+Send {
180 /// Forwards to the method defined on the type `Any`.
181 #[stable(feature = "rust1", since = "1.0.0")]
182 #[inline]
183 pub fn is<T: Any>(&self) -> bool {
184 Any::is::<T>(self)
185 }
186
187 /// Forwards to the method defined on the type `Any`.
188 #[stable(feature = "rust1", since = "1.0.0")]
189 #[inline]
190 pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
191 Any::downcast_ref::<T>(self)
192 }
193
194 /// Forwards to the method defined on the type `Any`.
195 #[stable(feature = "rust1", since = "1.0.0")]
196 #[inline]
197 pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> {
198 Any::downcast_mut::<T>(self)
199 }
200 }
201
202
203 ///////////////////////////////////////////////////////////////////////////////
204 // TypeID and its methods
205 ///////////////////////////////////////////////////////////////////////////////
206
207 /// A `TypeId` represents a globally unique identifier for a type.
208 ///
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.
212 ///
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")]
217 pub struct TypeId {
218 t: u64,
219 }
220
221 impl TypeId {
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 {
226 TypeId {
227 t: unsafe { intrinsics::type_id::<T>() },
228 }
229 }
230 }