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 //! 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 intrinsics;
  76
  77 ///////////////////////////////////////////////////////////////////////////////
  78 // Any trait
  79 ///////////////////////////////////////////////////////////////////////////////
  80
  81 /// A type to emulate dynamic typing.
  82 ///
  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.
  85 ///
  86 /// [mod]: index.html
  87 #[stable(feature = "rust1", since = "1.0.0")]
  88 pub trait Any: 'static {
  89     /// Gets the `TypeId` of `self`.
  90     ///
  91     /// # Examples
  92     ///
  93     /// ```
  94     /// #![feature(get_type_id)]
  95     ///
  96     /// use std::any::{Any, TypeId};
  97     ///
  98     /// fn is_string(s: &Any) -> bool {
  99     ///     TypeId::of::<String>() == s.get_type_id()
 100     /// }
 101     ///
 102     /// fn main() {
 103     ///     assert_eq!(is_string(&0), false);
 104     ///     assert_eq!(is_string(&"cookie monster".to_string()), true);
 105     /// }
 106     /// ```
 107     #[unstable(feature = "get_type_id",
 108                reason = "this method will likely be replaced by an associated static",
 109                issue = "27745")]
 110     fn get_type_id(&self) -> TypeId;
 111 }
 112
 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>() }
 116 }
 117
 118 ///////////////////////////////////////////////////////////////////////////////
 119 // Extension methods for Any trait objects.
 120 ///////////////////////////////////////////////////////////////////////////////
 121
 122 #[stable(feature = "rust1", since = "1.0.0")]
 123 impl fmt::Debug for Any {
 124     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 125         f.pad("Any")
 126     }
 127 }
 128
 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 {
 135         f.pad("Any")
 136     }
 137 }
 138
 139 #[stable(feature = "any_send_sync_methods", since = "1.28.0")]
 140 impl fmt::Debug for Any + Send + Sync {
 141     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 142         f.pad("Any")
 143     }
 144 }
 145
 146 impl Any {
 147     /// Returns `true` if the boxed type is the same as `T`.
 148     ///
 149     /// # Examples
 150     ///
 151     /// ```
 152     /// use std::any::Any;
 153     ///
 154     /// fn is_string(s: &Any) {
 155     ///     if s.is::<String>() {
 156     ///         println!("It's a string!");
 157     ///     } else {
 158     ///         println!("Not a string...");
 159     ///     }
 160     /// }
 161     ///
 162     /// fn main() {
 163     ///     is_string(&0);
 164     ///     is_string(&"cookie monster".to_string());
 165     /// }
 166     /// ```
 167     #[stable(feature = "rust1", since = "1.0.0")]
 168     #[inline]
 169     pub fn is<T: Any>(&self) -> bool {
 170         // Get TypeId of the type this function is instantiated with
 171         let t = TypeId::of::<T>();
 172
 173         // Get TypeId of the type in the trait object
 174         let boxed = self.get_type_id();
 175
 176         // Compare both TypeIds on equality
 177         t == boxed
 178     }
 179
 180     /// Returns some reference to the boxed value if it is of type `T`, or
 181     /// `None` if it isn't.
 182     ///
 183     /// # Examples
 184     ///
 185     /// ```
 186     /// use std::any::Any;
 187     ///
 188     /// fn print_if_string(s: &Any) {
 189     ///     if let Some(string) = s.downcast_ref::<String>() {
 190     ///         println!("It's a string({}): '{}'", string.len(), string);
 191     ///     } else {
 192     ///         println!("Not a string...");
 193     ///     }
 194     /// }
 195     ///
 196     /// fn main() {
 197     ///     print_if_string(&0);
 198     ///     print_if_string(&"cookie monster".to_string());
 199     /// }
 200     /// ```
 201     #[stable(feature = "rust1", since = "1.0.0")]
 202     #[inline]
 203     pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
 204         if self.is::<T>() {
 205             unsafe {
 206                 Some(&*(self as *const Any as *const T))
 207             }
 208         } else {
 209             None
 210         }
 211     }
 212
 213     /// Returns some mutable reference to the boxed value if it is of type `T`, or
 214     /// `None` if it isn't.
 215     ///
 216     /// # Examples
 217     ///
 218     /// ```
 219     /// use std::any::Any;
 220     ///
 221     /// fn modify_if_u32(s: &mut Any) {
 222     ///     if let Some(num) = s.downcast_mut::<u32>() {
 223     ///         *num = 42;
 224     ///     }
 225     /// }
 226     ///
 227     /// fn main() {
 228     ///     let mut x = 10u32;
 229     ///     let mut s = "starlord".to_string();
 230     ///
 231     ///     modify_if_u32(&mut x);
 232     ///     modify_if_u32(&mut s);
 233     ///
 234     ///     assert_eq!(x, 42);
 235     ///     assert_eq!(&s, "starlord");
 236     /// }
 237     /// ```
 238     #[stable(feature = "rust1", since = "1.0.0")]
 239     #[inline]
 240     pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> {
 241         if self.is::<T>() {
 242             unsafe {
 243                 Some(&mut *(self as *mut Any as *mut T))
 244             }
 245         } else {
 246             None
 247         }
 248     }
 249 }
 250
 251 impl Any+Send {
 252     /// Forwards to the method defined on the type `Any`.
 253     ///
 254     /// # Examples
 255     ///
 256     /// ```
 257     /// use std::any::Any;
 258     ///
 259     /// fn is_string(s: &(Any + Send)) {
 260     ///     if s.is::<String>() {
 261     ///         println!("It's a string!");
 262     ///     } else {
 263     ///         println!("Not a string...");
 264     ///     }
 265     /// }
 266     ///
 267     /// fn main() {
 268     ///     is_string(&0);
 269     ///     is_string(&"cookie monster".to_string());
 270     /// }
 271     /// ```
 272     #[stable(feature = "rust1", since = "1.0.0")]
 273     #[inline]
 274     pub fn is<T: Any>(&self) -> bool {
 275         Any::is::<T>(self)
 276     }
 277
 278     /// Forwards to the method defined on the type `Any`.
 279     ///
 280     /// # Examples
 281     ///
 282     /// ```
 283     /// use std::any::Any;
 284     ///
 285     /// fn print_if_string(s: &(Any + Send)) {
 286     ///     if let Some(string) = s.downcast_ref::<String>() {
 287     ///         println!("It's a string({}): '{}'", string.len(), string);
 288     ///     } else {
 289     ///         println!("Not a string...");
 290     ///     }
 291     /// }
 292     ///
 293     /// fn main() {
 294     ///     print_if_string(&0);
 295     ///     print_if_string(&"cookie monster".to_string());
 296     /// }
 297     /// ```
 298     #[stable(feature = "rust1", since = "1.0.0")]
 299     #[inline]
 300     pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
 301         Any::downcast_ref::<T>(self)
 302     }
 303
 304     /// Forwards to the method defined on the type `Any`.
 305     ///
 306     /// # Examples
 307     ///
 308     /// ```
 309     /// use std::any::Any;
 310     ///
 311     /// fn modify_if_u32(s: &mut (Any + Send)) {
 312     ///     if let Some(num) = s.downcast_mut::<u32>() {
 313     ///         *num = 42;
 314     ///     }
 315     /// }
 316     ///
 317     /// fn main() {
 318     ///     let mut x = 10u32;
 319     ///     let mut s = "starlord".to_string();
 320     ///
 321     ///     modify_if_u32(&mut x);
 322     ///     modify_if_u32(&mut s);
 323     ///
 324     ///     assert_eq!(x, 42);
 325     ///     assert_eq!(&s, "starlord");
 326     /// }
 327     /// ```
 328     #[stable(feature = "rust1", since = "1.0.0")]
 329     #[inline]
 330     pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> {
 331         Any::downcast_mut::<T>(self)
 332     }
 333 }
 334
 335 impl Any+Send+Sync {
 336     /// Forwards to the method defined on the type `Any`.
 337     ///
 338     /// # Examples
 339     ///
 340     /// ```
 341     /// use std::any::Any;
 342     ///
 343     /// fn is_string(s: &(Any + Send + Sync)) {
 344     ///     if s.is::<String>() {
 345     ///         println!("It's a string!");
 346     ///     } else {
 347     ///         println!("Not a string...");
 348     ///     }
 349     /// }
 350     ///
 351     /// fn main() {
 352     ///     is_string(&0);
 353     ///     is_string(&"cookie monster".to_string());
 354     /// }
 355     /// ```
 356     #[stable(feature = "any_send_sync_methods", since = "1.28.0")]
 357     #[inline]
 358     pub fn is<T: Any>(&self) -> bool {
 359         Any::is::<T>(self)
 360     }
 361
 362     /// Forwards to the method defined on the type `Any`.
 363     ///
 364     /// # Examples
 365     ///
 366     /// ```
 367     /// use std::any::Any;
 368     ///
 369     /// fn print_if_string(s: &(Any + Send + Sync)) {
 370     ///     if let Some(string) = s.downcast_ref::<String>() {
 371     ///         println!("It's a string({}): '{}'", string.len(), string);
 372     ///     } else {
 373     ///         println!("Not a string...");
 374     ///     }
 375     /// }
 376     ///
 377     /// fn main() {
 378     ///     print_if_string(&0);
 379     ///     print_if_string(&"cookie monster".to_string());
 380     /// }
 381     /// ```
 382     #[stable(feature = "any_send_sync_methods", since = "1.28.0")]
 383     #[inline]
 384     pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
 385         Any::downcast_ref::<T>(self)
 386     }
 387
 388     /// Forwards to the method defined on the type `Any`.
 389     ///
 390     /// # Examples
 391     ///
 392     /// ```
 393     /// use std::any::Any;
 394     ///
 395     /// fn modify_if_u32(s: &mut (Any + Send + Sync)) {
 396     ///     if let Some(num) = s.downcast_mut::<u32>() {
 397     ///         *num = 42;
 398     ///     }
 399     /// }
 400     ///
 401     /// fn main() {
 402     ///     let mut x = 10u32;
 403     ///     let mut s = "starlord".to_string();
 404     ///
 405     ///     modify_if_u32(&mut x);
 406     ///     modify_if_u32(&mut s);
 407     ///
 408     ///     assert_eq!(x, 42);
 409     ///     assert_eq!(&s, "starlord");
 410     /// }
 411     /// ```
 412     #[stable(feature = "any_send_sync_methods", since = "1.28.0")]
 413     #[inline]
 414     pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> {
 415         Any::downcast_mut::<T>(self)
 416     }
 417 }
 418
 419 ///////////////////////////////////////////////////////////////////////////////
 420 // TypeID and its methods
 421 ///////////////////////////////////////////////////////////////////////////////
 422
 423 /// A `TypeId` represents a globally unique identifier for a type.
 424 ///
 425 /// Each `TypeId` is an opaque object which does not allow inspection of what's
 426 /// inside but does allow basic operations such as cloning, comparison,
 427 /// printing, and showing.
 428 ///
 429 /// A `TypeId` is currently only available for types which ascribe to `'static`,
 430 /// but this limitation may be removed in the future.
 431 ///
 432 /// While `TypeId` implements `Hash`, `PartialOrd`, and `Ord`, it is worth
 433 /// noting that the hashes and ordering will vary between Rust releases. Beware
 434 /// of relying on them outside of your code!
 435 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
 436 #[stable(feature = "rust1", since = "1.0.0")]
 437 pub struct TypeId {
 438     t: u64,
 439 }
 440
 441 impl TypeId {
 442     /// Returns the `TypeId` of the type this generic function has been
 443     /// instantiated with.
 444     ///
 445     /// # Examples
 446     ///
 447     /// ```
 448     /// use std::any::{Any, TypeId};
 449     ///
 450     /// fn is_string<T: ?Sized + Any>(_s: &T) -> bool {
 451     ///     TypeId::of::<String>() == TypeId::of::<T>()
 452     /// }
 453     ///
 454     /// fn main() {
 455     ///     assert_eq!(is_string(&0), false);
 456     ///     assert_eq!(is_string(&"cookie monster".to_string()), true);
 457     /// }
 458     /// ```
 459     #[stable(feature = "rust1", since = "1.0.0")]
 460     #[rustc_const_unstable(feature="const_type_id")]
 461     pub const fn of<T: ?Sized + 'static>() -> TypeId {
 462         TypeId {
 463             t: unsafe { intrinsics::type_id::<T>() },
 464         }
 465     }
 466 }