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 //! Traits for dynamic typing of any `'static` type (through runtime reflection)
13 //! This module implements the `Any` trait, which enables dynamic typing
14 //! of any `'static` type through runtime reflection.
16 //! `Any` itself can be used to get a `TypeId`, and has more features when used
17 //! as a trait object. As `&Any` (a borrowed trait object), it has the `is` and
18 //! `as_ref` methods, to test if the contained value is of a given type, and to
19 //! get a reference to the inner value as a type. As`&mut Any`, there is also
20 //! the `as_mut` method, for getting a mutable reference to the inner value.
21 //! `Box<Any>` adds the `move` method, which will unwrap a `Box<T>` from the
22 //! object. See the extension traits (`*Ext`) for the full details.
24 //! Note that &Any is limited to testing whether a value is of a specified
25 //! concrete type, and cannot be used to test whether a type implements a trait.
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 Show, 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::Show;
38 //! use std::any::{Any, AnyRefExt};
40 //! // Logger function for any type that implements Show.
41 //! fn log<T: Any+Show>(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: Show+'static>(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;
75 use option::{Option, Some, None};
77 use intrinsics::TypeId;
79 ///////////////////////////////////////////////////////////////////////////////
81 ///////////////////////////////////////////////////////////////////////////////
83 /// The `Any` trait is implemented by all `'static` types, and can be used for
86 /// Every type with no non-`'static` references implements `Any`, so `Any` can
87 /// be used as a trait object to emulate the effects dynamic typing.
89 pub trait Any: 'static {
90 /// Get the `TypeId` of `self`
91 #[experimental = "this method will likely be replaced by an associated static"]
92 fn get_type_id(&self) -> TypeId;
95 impl<T: 'static> Any for T {
96 fn get_type_id(&self) -> TypeId { TypeId::of::<T>() }
99 ///////////////////////////////////////////////////////////////////////////////
100 // Extension methods for Any trait objects.
101 // Implemented as three extension traits so that the methods can be generic.
102 ///////////////////////////////////////////////////////////////////////////////
104 /// Extension methods for a referenced `Any` trait object
105 #[unstable = "this trait will not be necessary once DST lands, it will be a \
107 pub trait AnyRefExt<'a> {
108 /// Returns true if the boxed type is the same as `T`
110 fn is<T: 'static>(self) -> bool;
112 /// Returns some reference to the boxed value if it is of type `T`, or
113 /// `None` if it isn't.
114 #[unstable = "naming conventions around acquiring references may change"]
115 fn downcast_ref<T: 'static>(self) -> Option<&'a T>;
119 impl<'a> AnyRefExt<'a> for &'a Any {
121 fn is<T: 'static>(self) -> bool {
122 // Get TypeId of the type this function is instantiated with
123 let t = TypeId::of::<T>();
125 // Get TypeId of the type in the trait object
126 let boxed = self.get_type_id();
128 // Compare both TypeIds on equality
133 fn downcast_ref<T: 'static>(self) -> Option<&'a T> {
136 // Get the raw representation of the trait object
137 let to: TraitObject = transmute(self);
139 // Extract the data pointer
140 Some(transmute(to.data))
148 /// Extension methods for a mutable referenced `Any` trait object
149 #[unstable = "this trait will not be necessary once DST lands, it will be a \
151 pub trait AnyMutRefExt<'a> {
152 /// Returns some mutable reference to the boxed value if it is of type `T`, or
153 /// `None` if it isn't.
154 #[unstable = "naming conventions around acquiring references may change"]
155 fn downcast_mut<T: 'static>(self) -> Option<&'a mut T>;
159 impl<'a> AnyMutRefExt<'a> for &'a mut Any {
161 fn downcast_mut<T: 'static>(self) -> Option<&'a mut T> {
164 // Get the raw representation of the trait object
165 let to: TraitObject = transmute(self);
167 // Extract the data pointer
168 Some(transmute(to.data))