Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1067 insertions, 0 deletions

diff --git a/library/core/src/any.rs b/library/core/src/any.rs
new file mode 100644
index 000000000..f20c497a1
--- /dev/null
+++ b/library/core/src/any.rs
@@ -0,0 +1,1067 @@
+//! This module contains the `Any` trait, which enables dynamic typing
+//! of any `'static` type through runtime reflection. It also contains the
+//! `Provider` trait and accompanying API, which enable trait objects to provide
+//! data based on typed requests, an alternate form of runtime reflection.
+//!
+//! # `Any` and `TypeId`
+//!
+//! `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
+//!
+//! # Smart pointers and `dyn Any`
+//!
+//! One piece of behavior to keep in mind when using `Any` as a trait object,
+//! especially with types like `Box<dyn Any>` or `Arc<dyn Any>`, is that simply
+//! calling `.type_id()` on the value will produce the `TypeId` of the
+//! *container*, not the underlying trait object. This can be avoided by
+//! converting the smart pointer into a `&dyn Any` instead, which will return
+//! the object's `TypeId`. For example:
+//!
+//! ```
+//! use std::any::{Any, TypeId};
+//!
+//! let boxed: Box<dyn Any> = Box::new(3_i32);
+//!
+//! // You're more likely to want this:
+//! let actual_id = (&*boxed).type_id();
+//! // ... than this:
+//! let boxed_id = boxed.type_id();
+//!
+//! assert_eq!(actual_id, TypeId::of::<i32>());
+//! assert_eq!(boxed_id, TypeId::of::<Box<dyn Any>>());
+//! ```
+//!
+//! ## 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);
+//! }
+//! ```
+//!
+//! # `Provider` and `Demand`
+//!
+//! `Provider` and the associated APIs support generic, type-driven access to data, and a mechanism
+//! for implementers to provide such data. The key parts of the interface are the `Provider`
+//! trait for objects which can provide data, and the [`request_value`] and [`request_ref`]
+//! functions for requesting data from an object which implements `Provider`. Generally, end users
+//! should not call `request_*` directly, they are helper functions for intermediate implementers
+//! to use to implement a user-facing interface. This is purely for the sake of ergonomics, there is
+//! no safety concern here; intermediate implementers can typically support methods rather than
+//! free functions and use more specific names.
+//!
+//! Typically, a data provider is a trait object of a trait which extends `Provider`. A user will
+//! request data from a trait object by specifying the type of the data.
+//!
+//! ## Data flow
+//!
+//! * A user requests an object of a specific type, which is delegated to `request_value` or
+//!   `request_ref`
+//! * `request_*` creates a `Demand` object and passes it to `Provider::provide`
+//! * The data provider's implementation of `Provider::provide` tries providing values of
+//!   different types using `Demand::provide_*`. If the type matches the type requested by
+//!   the user, the value will be stored in the `Demand` object.
+//! * `request_*` unpacks the `Demand` object and returns any stored value to the user.
+//!
+//! ## Examples
+//!
+//! ```
+//! # #![feature(provide_any)]
+//! use std::any::{Provider, Demand, request_ref};
+//!
+//! // Definition of MyTrait, a data provider.
+//! trait MyTrait: Provider {
+//!     // ...
+//! }
+//!
+//! // Methods on `MyTrait` trait objects.
+//! impl dyn MyTrait + '_ {
+//!     /// Get a reference to a field of the implementing struct.
+//!     pub fn get_context_by_ref<T: ?Sized + 'static>(&self) -> Option<&T> {
+//!         request_ref::<T>(self)
+//!     }
+//! }
+//!
+//! // Downstream implementation of `MyTrait` and `Provider`.
+//! # struct SomeConcreteType { some_string: String }
+//! impl MyTrait for SomeConcreteType {
+//!     // ...
+//! }
+//!
+//! impl Provider for SomeConcreteType {
+//!     fn provide<'a>(&'a self, demand: &mut Demand<'a>) {
+//!         // Provide a string reference. We could provide multiple values with
+//!         // different types here.
+//!         demand.provide_ref::<String>(&self.some_string);
+//!     }
+//! }
+//!
+//! // Downstream usage of `MyTrait`.
+//! fn use_my_trait(obj: &dyn MyTrait) {
+//!     // Request a &String from obj.
+//!     let _ = obj.get_context_by_ref::<String>().unwrap();
+//! }
+//! ```
+//!
+//! In this example, if the concrete type of `obj` in `use_my_trait` is `SomeConcreteType`, then
+//! the `get_context_ref` call will return a reference to `obj.some_string` with type `&String`.
+
+#![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]: crate::any
+// 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")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "Any")]
+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.debug_struct("Any").finish_non_exhaustive()
+    }
+}
+
+// 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.debug_struct("Any").finish_non_exhaustive()
+    }
+}
+
+#[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.debug_struct("Any").finish_non_exhaustive()
+    }
+}
+
+impl dyn Any {
+    /// Returns `true` if the inner 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 inner 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.downcast_ref_unchecked()) }
+        } else {
+            None
+        }
+    }
+
+    /// Returns some mutable reference to the inner 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(self.downcast_mut_unchecked()) }
+        } else {
+            None
+        }
+    }
+
+    /// Returns a reference to the inner value as type `dyn T`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(downcast_unchecked)]
+    ///
+    /// use std::any::Any;
+    ///
+    /// let x: Box<dyn Any> = Box::new(1_usize);
+    ///
+    /// unsafe {
+    ///     assert_eq!(*x.downcast_ref_unchecked::<usize>(), 1);
+    /// }
+    /// ```
+    ///
+    /// # Safety
+    ///
+    /// The contained value must be of type `T`. Calling this method
+    /// with the incorrect type is *undefined behavior*.
+    #[unstable(feature = "downcast_unchecked", issue = "90850")]
+    #[inline]
+    pub unsafe fn downcast_ref_unchecked<T: Any>(&self) -> &T {
+        debug_assert!(self.is::<T>());
+        // SAFETY: caller guarantees that T is the correct type
+        unsafe { &*(self as *const dyn Any as *const T) }
+    }
+
+    /// Returns a mutable reference to the inner value as type `dyn T`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(downcast_unchecked)]
+    ///
+    /// use std::any::Any;
+    ///
+    /// let mut x: Box<dyn Any> = Box::new(1_usize);
+    ///
+    /// unsafe {
+    ///     *x.downcast_mut_unchecked::<usize>() += 1;
+    /// }
+    ///
+    /// assert_eq!(*x.downcast_ref::<usize>().unwrap(), 2);
+    /// ```
+    ///
+    /// # Safety
+    ///
+    /// The contained value must be of type `T`. Calling this method
+    /// with the incorrect type is *undefined behavior*.
+    #[unstable(feature = "downcast_unchecked", issue = "90850")]
+    #[inline]
+    pub unsafe fn downcast_mut_unchecked<T: Any>(&mut self) -> &mut T {
+        debug_assert!(self.is::<T>());
+        // SAFETY: caller guarantees that T is the correct type
+        unsafe { &mut *(self as *mut dyn Any as *mut T) }
+    }
+}
+
+impl dyn Any + Send {
+    /// Forwards to the method defined on the type `dyn 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 {
+        <dyn Any>::is::<T>(self)
+    }
+
+    /// Forwards to the method defined on the type `dyn 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> {
+        <dyn Any>::downcast_ref::<T>(self)
+    }
+
+    /// Forwards to the method defined on the type `dyn 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> {
+        <dyn Any>::downcast_mut::<T>(self)
+    }
+
+    /// Forwards to the method defined on the type `dyn Any`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(downcast_unchecked)]
+    ///
+    /// use std::any::Any;
+    ///
+    /// let x: Box<dyn Any> = Box::new(1_usize);
+    ///
+    /// unsafe {
+    ///     assert_eq!(*x.downcast_ref_unchecked::<usize>(), 1);
+    /// }
+    /// ```
+    ///
+    /// # Safety
+    ///
+    /// Same as the method on the type `dyn Any`.
+    #[unstable(feature = "downcast_unchecked", issue = "90850")]
+    #[inline]
+    pub unsafe fn downcast_ref_unchecked<T: Any>(&self) -> &T {
+        // SAFETY: guaranteed by caller
+        unsafe { <dyn Any>::downcast_ref_unchecked::<T>(self) }
+    }
+
+    /// Forwards to the method defined on the type `dyn Any`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(downcast_unchecked)]
+    ///
+    /// use std::any::Any;
+    ///
+    /// let mut x: Box<dyn Any> = Box::new(1_usize);
+    ///
+    /// unsafe {
+    ///     *x.downcast_mut_unchecked::<usize>() += 1;
+    /// }
+    ///
+    /// assert_eq!(*x.downcast_ref::<usize>().unwrap(), 2);
+    /// ```
+    ///
+    /// # Safety
+    ///
+    /// Same as the method on the type `dyn Any`.
+    #[unstable(feature = "downcast_unchecked", issue = "90850")]
+    #[inline]
+    pub unsafe fn downcast_mut_unchecked<T: Any>(&mut self) -> &mut T {
+        // SAFETY: guaranteed by caller
+        unsafe { <dyn Any>::downcast_mut_unchecked::<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 {
+        <dyn 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> {
+        <dyn 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> {
+        <dyn Any>::downcast_mut::<T>(self)
+    }
+
+    /// Forwards to the method defined on the type `Any`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(downcast_unchecked)]
+    ///
+    /// use std::any::Any;
+    ///
+    /// let x: Box<dyn Any> = Box::new(1_usize);
+    ///
+    /// unsafe {
+    ///     assert_eq!(*x.downcast_ref_unchecked::<usize>(), 1);
+    /// }
+    /// ```
+    #[unstable(feature = "downcast_unchecked", issue = "90850")]
+    #[inline]
+    pub unsafe fn downcast_ref_unchecked<T: Any>(&self) -> &T {
+        // SAFETY: guaranteed by caller
+        unsafe { <dyn Any>::downcast_ref_unchecked::<T>(self) }
+    }
+
+    /// Forwards to the method defined on the type `Any`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(downcast_unchecked)]
+    ///
+    /// use std::any::Any;
+    ///
+    /// let mut x: Box<dyn Any> = Box::new(1_usize);
+    ///
+    /// unsafe {
+    ///     *x.downcast_mut_unchecked::<usize>() += 1;
+    /// }
+    ///
+    /// assert_eq!(*x.downcast_ref::<usize>().unwrap(), 2);
+    /// ```
+    #[unstable(feature = "downcast_unchecked", issue = "90850")]
+    #[inline]
+    pub unsafe fn downcast_mut_unchecked<T: Any>(&mut self) -> &mut T {
+        // SAFETY: guaranteed by caller
+        unsafe { <dyn Any>::downcast_mut_unchecked::<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);
+    /// ```
+    #[must_use]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_unstable(feature = "const_type_id", issue = "77125")]
+    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>",
+/// );
+/// ```
+#[must_use]
+#[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));
+/// ```
+#[must_use]
+#[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>()
+}
+
+///////////////////////////////////////////////////////////////////////////////
+// Provider trait
+///////////////////////////////////////////////////////////////////////////////
+
+/// Trait implemented by a type which can dynamically provide values based on type.
+#[unstable(feature = "provide_any", issue = "96024")]
+pub trait Provider {
+    /// Data providers should implement this method to provide *all* values they are able to
+    /// provide by using `demand`.
+    ///
+    /// Note that the `provide_*` methods on `Demand` have short-circuit semantics: if an earlier
+    /// method has successfully provided a value, then later methods will not get an opportunity to
+    /// provide.
+    ///
+    /// # Examples
+    ///
+    /// Provides a reference to a field with type `String` as a `&str`, and a value of
+    /// type `i32`.
+    ///
+    /// ```rust
+    /// # #![feature(provide_any)]
+    /// use std::any::{Provider, Demand};
+    /// # struct SomeConcreteType { field: String, num_field: i32 }
+    ///
+    /// impl Provider for SomeConcreteType {
+    ///     fn provide<'a>(&'a self, demand: &mut Demand<'a>) {
+    ///         demand.provide_ref::<str>(&self.field)
+    ///             .provide_value::<i32>(|| self.num_field);
+    ///     }
+    /// }
+    /// ```
+    #[unstable(feature = "provide_any", issue = "96024")]
+    fn provide<'a>(&'a self, demand: &mut Demand<'a>);
+}
+
+/// Request a value from the `Provider`.
+///
+/// # Examples
+///
+/// Get a string value from a provider.
+///
+/// ```rust
+/// # #![feature(provide_any)]
+/// use std::any::{Provider, request_value};
+///
+/// fn get_string(provider: &impl Provider) -> String {
+///     request_value::<String>(provider).unwrap()
+/// }
+/// ```
+#[unstable(feature = "provide_any", issue = "96024")]
+pub fn request_value<'a, T>(provider: &'a (impl Provider + ?Sized)) -> Option<T>
+where
+    T: 'static,
+{
+    request_by_type_tag::<'a, tags::Value<T>>(provider)
+}
+
+/// Request a reference from the `Provider`.
+///
+/// # Examples
+///
+/// Get a string reference from a provider.
+///
+/// ```rust
+/// # #![feature(provide_any)]
+/// use std::any::{Provider, request_ref};
+///
+/// fn get_str(provider: &impl Provider) -> &str {
+///     request_ref::<str>(provider).unwrap()
+/// }
+/// ```
+#[unstable(feature = "provide_any", issue = "96024")]
+pub fn request_ref<'a, T>(provider: &'a (impl Provider + ?Sized)) -> Option<&'a T>
+where
+    T: 'static + ?Sized,
+{
+    request_by_type_tag::<'a, tags::Ref<tags::MaybeSizedValue<T>>>(provider)
+}
+
+/// Request a specific value by tag from the `Provider`.
+fn request_by_type_tag<'a, I>(provider: &'a (impl Provider + ?Sized)) -> Option<I::Reified>
+where
+    I: tags::Type<'a>,
+{
+    let mut tagged = TaggedOption::<'a, I>(None);
+    provider.provide(tagged.as_demand());
+    tagged.0
+}
+
+///////////////////////////////////////////////////////////////////////////////
+// Demand and its methods
+///////////////////////////////////////////////////////////////////////////////
+
+/// A helper object for providing data by type.
+///
+/// A data provider provides values by calling this type's provide methods.
+#[unstable(feature = "provide_any", issue = "96024")]
+#[repr(transparent)]
+pub struct Demand<'a>(dyn Erased<'a> + 'a);
+
+impl<'a> Demand<'a> {
+    /// Create a new `&mut Demand` from a `&mut dyn Erased` trait object.
+    fn new<'b>(erased: &'b mut (dyn Erased<'a> + 'a)) -> &'b mut Demand<'a> {
+        // SAFETY: transmuting `&mut (dyn Erased<'a> + 'a)` to `&mut Demand<'a>` is safe since
+        // `Demand` is repr(transparent).
+        unsafe { &mut *(erased as *mut dyn Erased<'a> as *mut Demand<'a>) }
+    }
+
+    /// Provide a value or other type with only static lifetimes.
+    ///
+    /// # Examples
+    ///
+    /// Provides a `String` by cloning.
+    ///
+    /// ```rust
+    /// # #![feature(provide_any)]
+    /// use std::any::{Provider, Demand};
+    /// # struct SomeConcreteType { field: String }
+    ///
+    /// impl Provider for SomeConcreteType {
+    ///     fn provide<'a>(&'a self, demand: &mut Demand<'a>) {
+    ///         demand.provide_value::<String>(|| self.field.clone());
+    ///     }
+    /// }
+    /// ```
+    #[unstable(feature = "provide_any", issue = "96024")]
+    pub fn provide_value<T>(&mut self, fulfil: impl FnOnce() -> T) -> &mut Self
+    where
+        T: 'static,
+    {
+        self.provide_with::<tags::Value<T>>(fulfil)
+    }
+
+    /// Provide a reference, note that the referee type must be bounded by `'static`,
+    /// but may be unsized.
+    ///
+    /// # Examples
+    ///
+    /// Provides a reference to a field as a `&str`.
+    ///
+    /// ```rust
+    /// # #![feature(provide_any)]
+    /// use std::any::{Provider, Demand};
+    /// # struct SomeConcreteType { field: String }
+    ///
+    /// impl Provider for SomeConcreteType {
+    ///     fn provide<'a>(&'a self, demand: &mut Demand<'a>) {
+    ///         demand.provide_ref::<str>(&self.field);
+    ///     }
+    /// }
+    /// ```
+    #[unstable(feature = "provide_any", issue = "96024")]
+    pub fn provide_ref<T: ?Sized + 'static>(&mut self, value: &'a T) -> &mut Self {
+        self.provide::<tags::Ref<tags::MaybeSizedValue<T>>>(value)
+    }
+
+    /// Provide a value with the given `Type` tag.
+    fn provide<I>(&mut self, value: I::Reified) -> &mut Self
+    where
+        I: tags::Type<'a>,
+    {
+        if let Some(res @ TaggedOption(None)) = self.0.downcast_mut::<I>() {
+            res.0 = Some(value);
+        }
+        self
+    }
+
+    /// Provide a value with the given `Type` tag, using a closure to prevent unnecessary work.
+    fn provide_with<I>(&mut self, fulfil: impl FnOnce() -> I::Reified) -> &mut Self
+    where
+        I: tags::Type<'a>,
+    {
+        if let Some(res @ TaggedOption(None)) = self.0.downcast_mut::<I>() {
+            res.0 = Some(fulfil());
+        }
+        self
+    }
+}
+
+#[unstable(feature = "provide_any", issue = "96024")]
+impl<'a> fmt::Debug for Demand<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Demand").finish_non_exhaustive()
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////////
+// Type tags
+///////////////////////////////////////////////////////////////////////////////
+
+mod tags {
+    //! Type tags are used to identify a type using a separate value. This module includes type tags
+    //! for some very common types.
+    //!
+    //! Currently type tags are not exposed to the user. But in the future, if you want to use the
+    //! Provider API with more complex types (typically those including lifetime parameters), you
+    //! will need to write your own tags.
+
+    use crate::marker::PhantomData;
+
+    /// This trait is implemented by specific tag types in order to allow
+    /// describing a type which can be requested for a given lifetime `'a`.
+    ///
+    /// A few example implementations for type-driven tags can be found in this
+    /// module, although crates may also implement their own tags for more
+    /// complex types with internal lifetimes.
+    pub trait Type<'a>: Sized + 'static {
+        /// The type of values which may be tagged by this tag for the given
+        /// lifetime.
+        type Reified: 'a;
+    }
+
+    /// Similar to the [`Type`] trait, but represents a type which may be unsized (i.e., has a
+    /// `?Sized` bound). E.g., `str`.
+    pub trait MaybeSizedType<'a>: Sized + 'static {
+        type Reified: 'a + ?Sized;
+    }
+
+    impl<'a, T: Type<'a>> MaybeSizedType<'a> for T {
+        type Reified = T::Reified;
+    }
+
+    /// Type-based tag for types bounded by `'static`, i.e., with no borrowed elements.
+    #[derive(Debug)]
+    pub struct Value<T: 'static>(PhantomData<T>);
+
+    impl<'a, T: 'static> Type<'a> for Value<T> {
+        type Reified = T;
+    }
+
+    /// Type-based tag similar to [`Value`] but which may be unsized (i.e., has a `?Sized` bound).
+    #[derive(Debug)]
+    pub struct MaybeSizedValue<T: ?Sized + 'static>(PhantomData<T>);
+
+    impl<'a, T: ?Sized + 'static> MaybeSizedType<'a> for MaybeSizedValue<T> {
+        type Reified = T;
+    }
+
+    /// Type-based tag for reference types (`&'a T`, where T is represented by
+    /// `<I as MaybeSizedType<'a>>::Reified`.
+    #[derive(Debug)]
+    pub struct Ref<I>(PhantomData<I>);
+
+    impl<'a, I: MaybeSizedType<'a>> Type<'a> for Ref<I> {
+        type Reified = &'a I::Reified;
+    }
+}
+
+/// An `Option` with a type tag `I`.
+///
+/// Since this struct implements `Erased`, the type can be erased to make a dynamically typed
+/// option. The type can be checked dynamically using `Erased::tag_id` and since this is statically
+/// checked for the concrete type, there is some degree of type safety.
+#[repr(transparent)]
+struct TaggedOption<'a, I: tags::Type<'a>>(Option<I::Reified>);
+
+impl<'a, I: tags::Type<'a>> TaggedOption<'a, I> {
+    fn as_demand(&mut self) -> &mut Demand<'a> {
+        Demand::new(self as &mut (dyn Erased<'a> + 'a))
+    }
+}
+
+/// Represents a type-erased but identifiable object.
+///
+/// This trait is exclusively implemented by the `TaggedOption` type.
+unsafe trait Erased<'a>: 'a {
+    /// The `TypeId` of the erased type.
+    fn tag_id(&self) -> TypeId;
+}
+
+unsafe impl<'a, I: tags::Type<'a>> Erased<'a> for TaggedOption<'a, I> {
+    fn tag_id(&self) -> TypeId {
+        TypeId::of::<I>()
+    }
+}
+
+#[unstable(feature = "provide_any", issue = "96024")]
+impl<'a> dyn Erased<'a> + 'a {
+    /// Returns some reference to the dynamic value if it is tagged with `I`,
+    /// or `None` otherwise.
+    #[inline]
+    fn downcast_mut<I>(&mut self) -> Option<&mut TaggedOption<'a, I>>
+    where
+        I: tags::Type<'a>,
+    {
+        if self.tag_id() == TypeId::of::<I>() {
+            // SAFETY: Just checked whether we're pointing to an I.
+            Some(unsafe { &mut *(self as *mut Self).cast::<TaggedOption<'a, I>>() })
+        } else {
+            None
+        }
+    }
+}