src/libcore/any.rs

   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 //! Traits for dynamic typing of any `'static` type (through runtime reflection)
  12 //!
  13 //! This module implements the `Any` trait, which enables dynamic typing
  14 //! of any `'static` type through runtime reflection.
  15 //!
  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.
  23 //!
  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.
  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. See the [module-level documentation][mod] for more details.
  87 ///
  88 /// Every type with no non-`'static` references implements `Any`.
  89 ///
  90 /// [mod]: ../index.html
  91 #[stable(feature = "rust1", since = "1.0.0")]
  92 pub trait Any: Reflect + 'static {
  93     /// Get the `TypeId` of `self`
  94     #[unstable(feature = "core",
  95                reason = "this method will likely be replaced by an associated static")]
  96     fn get_type_id(&self) -> TypeId;
  97 }
  98
  99 impl<T> Any for T
 100     where T: Reflect + 'static
 101 {
 102     fn get_type_id(&self) -> TypeId { TypeId::of::<T>() }
 103 }
 104
 105 ///////////////////////////////////////////////////////////////////////////////
 106 // Extension methods for Any trait objects.
 107 ///////////////////////////////////////////////////////////////////////////////
 108
 109 #[stable(feature = "rust1", since = "1.0.0")]
 110 impl fmt::Debug for Any {
 111     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 112         f.pad("Any")
 113     }
 114 }
 115
 116 impl Any {
 117     /// Returns true if the boxed type is the same as `T`
 118     #[stable(feature = "rust1", since = "1.0.0")]
 119     #[inline]
 120     pub fn is<T: Any>(&self) -> bool {
 121         // Get TypeId of the type this function is instantiated with
 122         let t = TypeId::of::<T>();
 123
 124         // Get TypeId of the type in the trait object
 125         let boxed = self.get_type_id();
 126
 127         // Compare both TypeIds on equality
 128         t == boxed
 129     }
 130
 131     /// Returns some reference to the boxed value if it is of type `T`, or
 132     /// `None` if it isn't.
 133     #[stable(feature = "rust1", since = "1.0.0")]
 134     #[inline]
 135     pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
 136         if self.is::<T>() {
 137             unsafe {
 138                 // Get the raw representation of the trait object
 139                 let to: TraitObject = transmute(self);
 140
 141                 // Extract the data pointer
 142                 Some(transmute(to.data))
 143             }
 144         } else {
 145             None
 146         }
 147     }
 148
 149     /// Returns some mutable reference to the boxed value if it is of type `T`, or
 150     /// `None` if it isn't.
 151     #[stable(feature = "rust1", since = "1.0.0")]
 152     #[inline]
 153     pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> {
 154         if self.is::<T>() {
 155             unsafe {
 156                 // Get the raw representation of the trait object
 157                 let to: TraitObject = transmute(self);
 158
 159                 // Extract the data pointer
 160                 Some(transmute(to.data))
 161             }
 162         } else {
 163             None
 164         }
 165     }
 166 }
 167
 168 impl Any+Send {
 169     /// Forwards to the method defined on the type `Any`.
 170     #[stable(feature = "rust1", since = "1.0.0")]
 171     #[inline]
 172     pub fn is<T: Any>(&self) -> bool {
 173         Any::is::<T>(self)
 174     }
 175
 176     /// Forwards to the method defined on the type `Any`.
 177     #[stable(feature = "rust1", since = "1.0.0")]
 178     #[inline]
 179     pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
 180         Any::downcast_ref::<T>(self)
 181     }
 182
 183     /// Forwards to the method defined on the type `Any`.
 184     #[stable(feature = "rust1", since = "1.0.0")]
 185     #[inline]
 186     pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> {
 187         Any::downcast_mut::<T>(self)
 188     }
 189 }
 190
 191
 192 ///////////////////////////////////////////////////////////////////////////////
 193 // TypeID and its methods
 194 ///////////////////////////////////////////////////////////////////////////////
 195
 196 /// A `TypeId` represents a globally unique identifier for a type.
 197 ///
 198 /// Each `TypeId` is an opaque object which does not allow inspection of what's
 199 /// inside but does allow basic operations such as cloning, comparison,
 200 /// printing, and showing.
 201 ///
 202 /// A `TypeId` is currently only available for types which ascribe to `'static`,
 203 /// but this limitation may be removed in the future.
 204 #[derive(Clone, Copy, PartialEq, Eq, Debug, Hash)]
 205 #[stable(feature = "rust1", since = "1.0.0")]
 206 pub struct TypeId {
 207     t: u64,
 208 }
 209
 210 impl TypeId {
 211     /// Returns the `TypeId` of the type this generic function has been
 212     /// instantiated with
 213     #[stable(feature = "rust1", since = "1.0.0")]
 214     pub fn of<T: ?Sized + Any>() -> TypeId {
 215         TypeId {
 216             t: unsafe { intrinsics::type_id::<T>() },
 217         }
 218     }
 219 }