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//! This module implements the `Any` trait, which enables dynamic typing //! of any `'static` type through runtime reflection. //! //! `Any` itself can be used to get a `TypeId`, and has more features when used //! as a trait object. As `&Any` (a borrowed trait object), it has the `is` and //! `downcast_ref` methods, to test if the contained value is of a given type, //! and to get a reference to the inner value as a type. As `&mut Any`, there //! is also the `downcast_mut` method, for getting a mutable reference to the //! inner value. `Box<Any>` adds the `downcast` method, which attempts to //! convert to a `Box<T>`. See the [`Box`] documentation for the full details. //! //! Note that &Any is limited to testing whether a value is of a specified //! concrete type, and cannot be used to test whether a type implements a trait. //! //! [`Box`]: ../../std/boxed/struct.Box.html //! //! # Examples //! //! Consider a situation where we want to log out a value passed to a function. //! We know the value we're working on implements Debug, but we don't know its //! concrete type. We want to give special treatment to certain types: in this //! case printing out the length of String values prior to their value. //! We don't know the concrete type of our value at compile time, so we need to //! use runtime reflection instead. //! //! ```rust //! use std::fmt::Debug; //! use std::any::Any; //! //! // Logger function for any type that implements Debug. //! fn log<T: Any + Debug>(value: &T) { //! let value_any = value as &dyn Any; //! //! // Try to convert our value to a `String`. If successful, we want to //! // output the String`'s length as well as its value. If not, it's a //! // different type: just print it out unadorned. //! match value_any.downcast_ref::<String>() { //! Some(as_string) => { //! println!("String ({}): {}", as_string.len(), as_string); //! } //! None => { //! println!("{:?}", value); //! } //! } //! } //! //! // This function wants to log its parameter out prior to doing work with it. //! fn do_work<T: Any + Debug>(value: &T) { //! log(value); //! // ...do some other work //! } //! //! fn main() { //! let my_string = "Hello World".to_string(); //! do_work(&my_string); //! //! let my_i8: i8 = 100; //! do_work(&my_i8); //! } //! ``` #![stable(feature = "rust1", since = "1.0.0")] use crate::fmt; use crate::intrinsics; /////////////////////////////////////////////////////////////////////////////// // Any trait /////////////////////////////////////////////////////////////////////////////// /// A type to emulate dynamic typing. /// /// Most types implement `Any`. However, any type which contains a non-`'static` reference does not. /// See the [module-level documentation][mod] for more details. /// /// [mod]: index.html #[stable(feature = "rust1", since = "1.0.0")] pub trait Any: 'static { /// Gets the `TypeId` of `self`. /// /// # Examples /// /// ``` /// use std::any::{Any, TypeId}; /// /// fn is_string(s: &dyn Any) -> bool { /// TypeId::of::<String>() == s.type_id() /// } /// /// fn main() { /// assert_eq!(is_string(&0), false); /// assert_eq!(is_string(&"cookie monster".to_string()), true); /// } /// ``` #[stable(feature = "get_type_id", since = "1.34.0")] fn type_id(&self) -> TypeId; } #[stable(feature = "rust1", since = "1.0.0")] impl<T: 'static + ?Sized > Any for T { fn type_id(&self) -> TypeId { TypeId::of::<T>() } } /////////////////////////////////////////////////////////////////////////////// // Extension methods for Any trait objects. /////////////////////////////////////////////////////////////////////////////// #[stable(feature = "rust1", since = "1.0.0")] impl fmt::Debug for dyn Any { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { f.pad("Any") } } // Ensure that the result of e.g., joining a thread can be printed and // hence used with `unwrap`. May eventually no longer be needed if // dispatch works with upcasting. #[stable(feature = "rust1", since = "1.0.0")] impl fmt::Debug for dyn Any + Send { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { f.pad("Any") } } #[stable(feature = "any_send_sync_methods", since = "1.28.0")] impl fmt::Debug for dyn Any + Send + Sync { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { f.pad("Any") } } impl dyn Any { /// Returns `true` if the boxed type is the same as `T`. /// /// # Examples /// /// ``` /// use std::any::Any; /// /// fn is_string(s: &dyn Any) { /// if s.is::<String>() { /// println!("It's a string!"); /// } else { /// println!("Not a string..."); /// } /// } /// /// fn main() { /// is_string(&0); /// is_string(&"cookie monster".to_string()); /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] #[inline] pub fn is<T: Any>(&self) -> bool { // Get `TypeId` of the type this function is instantiated with. let t = TypeId::of::<T>(); // Get `TypeId` of the type in the trait object. let concrete = self.type_id(); // Compare both `TypeId`s on equality. t == concrete } /// Returns some reference to the boxed value if it is of type `T`, or /// `None` if it isn't. /// /// # Examples /// /// ``` /// use std::any::Any; /// /// fn print_if_string(s: &dyn Any) { /// if let Some(string) = s.downcast_ref::<String>() { /// println!("It's a string({}): '{}'", string.len(), string); /// } else { /// println!("Not a string..."); /// } /// } /// /// fn main() { /// print_if_string(&0); /// print_if_string(&"cookie monster".to_string()); /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] #[inline] pub fn downcast_ref<T: Any>(&self) -> Option<&T> { if self.is::<T>() { unsafe { Some(&*(self as *const dyn Any as *const T)) } } else { None } } /// Returns some mutable reference to the boxed value if it is of type `T`, or /// `None` if it isn't. /// /// # Examples /// /// ``` /// use std::any::Any; /// /// fn modify_if_u32(s: &mut dyn Any) { /// if let Some(num) = s.downcast_mut::<u32>() { /// *num = 42; /// } /// } /// /// fn main() { /// let mut x = 10u32; /// let mut s = "starlord".to_string(); /// /// modify_if_u32(&mut x); /// modify_if_u32(&mut s); /// /// assert_eq!(x, 42); /// assert_eq!(&s, "starlord"); /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] #[inline] pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> { if self.is::<T>() { unsafe { Some(&mut *(self as *mut dyn Any as *mut T)) } } else { None } } } impl dyn Any+Send { /// Forwards to the method defined on the type `Any`. /// /// # Examples /// /// ``` /// use std::any::Any; /// /// fn is_string(s: &(dyn Any + Send)) { /// if s.is::<String>() { /// println!("It's a string!"); /// } else { /// println!("Not a string..."); /// } /// } /// /// fn main() { /// is_string(&0); /// is_string(&"cookie monster".to_string()); /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] #[inline] pub fn is<T: Any>(&self) -> bool { Any::is::<T>(self) } /// Forwards to the method defined on the type `Any`. /// /// # Examples /// /// ``` /// use std::any::Any; /// /// fn print_if_string(s: &(dyn Any + Send)) { /// if let Some(string) = s.downcast_ref::<String>() { /// println!("It's a string({}): '{}'", string.len(), string); /// } else { /// println!("Not a string..."); /// } /// } /// /// fn main() { /// print_if_string(&0); /// print_if_string(&"cookie monster".to_string()); /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] #[inline] pub fn downcast_ref<T: Any>(&self) -> Option<&T> { Any::downcast_ref::<T>(self) } /// Forwards to the method defined on the type `Any`. /// /// # Examples /// /// ``` /// use std::any::Any; /// /// fn modify_if_u32(s: &mut (dyn Any + Send)) { /// if let Some(num) = s.downcast_mut::<u32>() { /// *num = 42; /// } /// } /// /// fn main() { /// let mut x = 10u32; /// let mut s = "starlord".to_string(); /// /// modify_if_u32(&mut x); /// modify_if_u32(&mut s); /// /// assert_eq!(x, 42); /// assert_eq!(&s, "starlord"); /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] #[inline] pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> { Any::downcast_mut::<T>(self) } } impl dyn Any+Send+Sync { /// Forwards to the method defined on the type `Any`. /// /// # Examples /// /// ``` /// use std::any::Any; /// /// fn is_string(s: &(dyn Any + Send + Sync)) { /// if s.is::<String>() { /// println!("It's a string!"); /// } else { /// println!("Not a string..."); /// } /// } /// /// fn main() { /// is_string(&0); /// is_string(&"cookie monster".to_string()); /// } /// ``` #[stable(feature = "any_send_sync_methods", since = "1.28.0")] #[inline] pub fn is<T: Any>(&self) -> bool { Any::is::<T>(self) } /// Forwards to the method defined on the type `Any`. /// /// # Examples /// /// ``` /// use std::any::Any; /// /// fn print_if_string(s: &(dyn Any + Send + Sync)) { /// if let Some(string) = s.downcast_ref::<String>() { /// println!("It's a string({}): '{}'", string.len(), string); /// } else { /// println!("Not a string..."); /// } /// } /// /// fn main() { /// print_if_string(&0); /// print_if_string(&"cookie monster".to_string()); /// } /// ``` #[stable(feature = "any_send_sync_methods", since = "1.28.0")] #[inline] pub fn downcast_ref<T: Any>(&self) -> Option<&T> { Any::downcast_ref::<T>(self) } /// Forwards to the method defined on the type `Any`. /// /// # Examples /// /// ``` /// use std::any::Any; /// /// fn modify_if_u32(s: &mut (dyn Any + Send + Sync)) { /// if let Some(num) = s.downcast_mut::<u32>() { /// *num = 42; /// } /// } /// /// fn main() { /// let mut x = 10u32; /// let mut s = "starlord".to_string(); /// /// modify_if_u32(&mut x); /// modify_if_u32(&mut s); /// /// assert_eq!(x, 42); /// assert_eq!(&s, "starlord"); /// } /// ``` #[stable(feature = "any_send_sync_methods", since = "1.28.0")] #[inline] pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> { Any::downcast_mut::<T>(self) } } /////////////////////////////////////////////////////////////////////////////// // TypeID and its methods /////////////////////////////////////////////////////////////////////////////// /// A `TypeId` represents a globally unique identifier for a type. /// /// Each `TypeId` is an opaque object which does not allow inspection of what's /// inside but does allow basic operations such as cloning, comparison, /// printing, and showing. /// /// A `TypeId` is currently only available for types which ascribe to `'static`, /// but this limitation may be removed in the future. /// /// While `TypeId` implements `Hash`, `PartialOrd`, and `Ord`, it is worth /// noting that the hashes and ordering will vary between Rust releases. Beware /// of relying on them inside of your code! #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)] #[stable(feature = "rust1", since = "1.0.0")] pub struct TypeId { t: u64, } impl TypeId { /// Returns the `TypeId` of the type this generic function has been /// instantiated with. /// /// # Examples /// /// ``` /// use std::any::{Any, TypeId}; /// /// fn is_string<T: ?Sized + Any>(_s: &T) -> bool { /// TypeId::of::<String>() == TypeId::of::<T>() /// } /// /// fn main() { /// assert_eq!(is_string(&0), false); /// assert_eq!(is_string(&"cookie monster".to_string()), true); /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] #[rustc_const_unstable(feature="const_type_id")] pub const fn of<T: ?Sized + 'static>() -> TypeId { TypeId { t: unsafe { intrinsics::type_id::<T>() }, } } } /// Returns the name of a type as a string slice. /// /// # Note /// /// This is intended for diagnostic use. The exact contents and format of the /// string are not specified, other than being a best-effort description of the /// type. For example, `type_name::<Option<String>>()` could return the /// `"Option<String>"` or `"std::option::Option<std::string::String>"`, but not /// `"foobar"`. In addition, the output may change between versions of the /// compiler. /// /// The type name should not be considered a unique identifier of a type; /// multiple types may share the same type name. /// /// The current implementation uses the same infrastructure as compiler /// diagnostics and debuginfo, but this is not guaranteed. #[stable(feature = "type_name", since = "1.38.0")] #[rustc_const_unstable(feature = "const_type_name")] pub const fn type_name<T: ?Sized>() -> &'static str { intrinsics::type_name::<T>() }