diff options
Diffstat (limited to 'library/core/src/any.rs')
| -rw-r--r-- | library/core/src/any.rs | 517 |
1 files changed, 517 insertions, 0 deletions
diff --git a/library/core/src/any.rs b/library/core/src/any.rs new file mode 100644 index 00000000000..79b6304958d --- /dev/null +++ b/library/core/src/any.rs @@ -0,0 +1,517 @@ +//! 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 `&dyn 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 dyn Any`, there +//! is also the `downcast_mut` method, for getting a mutable reference to the +//! inner value. `Box<dyn Any>` adds the `downcast` method, which attempts to +//! convert to a `Box<T>`. See the [`Box`] documentation for the full details. +//! +//! Note that `&dyn 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 trait 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 +// This trait is not unsafe, though we rely on the specifics of it's sole impl's +// `type_id` function in unsafe code (e.g., `downcast`). Normally, that would be +// a problem, but because the only impl of `Any` is a blanket implementation, no +// other code can implement `Any`. +// +// We could plausibly make this trait unsafe -- it would not cause breakage, +// since we control all the implementations -- but we choose not to as that's +// both not really necessary and may confuse users about the distinction of +// unsafe traits and unsafe methods (i.e., `type_id` would still be safe to call, +// but we would likely want to indicate as such in documentation). +#[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() + /// } + /// + /// 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..."); + /// } + /// } + /// + /// 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 (`self`). + 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..."); + /// } + /// } + /// + /// 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>() { + // SAFETY: just checked whether we are pointing to the correct type, and we can rely on + // that check for memory safety because we have implemented Any for all types; no other + // impls can exist as they would conflict with our impl. + 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; + /// } + /// } + /// + /// 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>() { + // SAFETY: just checked whether we are pointing to the correct type, and we can rely on + // that check for memory safety because we have implemented Any for all types; no other + // impls can exist as they would conflict with our impl. + 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..."); + /// } + /// } + /// + /// 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..."); + /// } + /// } + /// + /// 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; + /// } + /// } + /// + /// 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..."); + /// } + /// } + /// + /// 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..."); + /// } + /// } + /// + /// 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; + /// } + /// } + /// + /// 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>() + /// } + /// + /// 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", issue = "41875")] + pub const fn of<T: ?Sized + 'static>() -> TypeId { + TypeId { t: 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 returned are not specified, other than being a best-effort +/// description of the type. For example, amongst the strings +/// that `type_name::<Option<String>>()` might return are `"Option<String>"` and +/// `"std::option::Option<std::string::String>"`. +/// +/// The returned string must not be considered to be a unique identifier of a +/// type as multiple types may map to the same type name. Similarly, there is no +/// guarantee that all parts of a type will appear in the returned string: for +/// example, lifetime specifiers are currently not included. In addition, the +/// output may change between versions of the compiler. +/// +/// The current implementation uses the same infrastructure as compiler +/// diagnostics and debuginfo, but this is not guaranteed. +/// +/// # Examples +/// +/// ```rust +/// assert_eq!( +/// std::any::type_name::<Option<String>>(), +/// "core::option::Option<alloc::string::String>", +/// ); +/// ``` +#[stable(feature = "type_name", since = "1.38.0")] +#[rustc_const_unstable(feature = "const_type_name", issue = "63084")] +pub const fn type_name<T: ?Sized>() -> &'static str { + intrinsics::type_name::<T>() +} + +/// Returns the name of the type of the pointed-to value as a string slice. +/// This is the same as `type_name::<T>()`, but can be used where the type of a +/// variable is not easily available. +/// +/// # 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_of_val::<Option<String>>(None)` could return +/// `"Option<String>"` or `"std::option::Option<std::string::String>"`, but not +/// `"foobar"`. In addition, the output may change between versions of the +/// compiler. +/// +/// This function does not resolve trait objects, +/// meaning that `type_name_of_val(&7u32 as &dyn Debug)` +/// may return `"dyn Debug"`, but not `"u32"`. +/// +/// 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. +/// +/// # Examples +/// +/// Prints the default integer and float types. +/// +/// ```rust +/// #![feature(type_name_of_val)] +/// use std::any::type_name_of_val; +/// +/// let x = 1; +/// println!("{}", type_name_of_val(&x)); +/// let y = 1.0; +/// println!("{}", type_name_of_val(&y)); +/// ``` +#[unstable(feature = "type_name_of_val", issue = "66359")] +#[rustc_const_unstable(feature = "const_type_name", issue = "63084")] +pub const fn type_name_of_val<T: ?Sized>(_val: &T) -> &'static str { + type_name::<T>() +} |