mirror of https://github.com/rust-lang/rust
742 lines
23 KiB
Rust
742 lines
23 KiB
Rust
//! Utilities for dynamic typing or type reflection.
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//!
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//! # `Any` and `TypeId`
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//!
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//! `Any` itself can be used to get a `TypeId`, and has more features when used
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//! as a trait object. As `&dyn Any` (a borrowed trait object), it has the `is`
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//! and `downcast_ref` methods, to test if the contained value is of a given type,
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//! and to get a reference to the inner value as a type. As `&mut dyn Any`, there
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//! is also the `downcast_mut` method, for getting a mutable reference to the
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//! inner value. `Box<dyn Any>` adds the `downcast` method, which attempts to
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//! convert to a `Box<T>`. See the [`Box`] documentation for the full details.
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//!
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//! Note that `&dyn Any` is limited to testing whether a value is of a specified
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//! concrete type, and cannot be used to test whether a type implements a trait.
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//!
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//! [`Box`]: ../../std/boxed/struct.Box.html
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//!
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//! # Smart pointers and `dyn Any`
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//!
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//! One piece of behavior to keep in mind when using `Any` as a trait object,
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//! especially with types like `Box<dyn Any>` or `Arc<dyn Any>`, is that simply
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//! calling `.type_id()` on the value will produce the `TypeId` of the
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//! *container*, not the underlying trait object. This can be avoided by
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//! converting the smart pointer into a `&dyn Any` instead, which will return
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//! the object's `TypeId`. For example:
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//!
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//! ```
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//! use std::any::{Any, TypeId};
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//!
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//! let boxed: Box<dyn Any> = Box::new(3_i32);
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//!
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//! // You're more likely to want this:
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//! let actual_id = (&*boxed).type_id();
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//! // ... than this:
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//! let boxed_id = boxed.type_id();
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//!
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//! assert_eq!(actual_id, TypeId::of::<i32>());
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//! assert_eq!(boxed_id, TypeId::of::<Box<dyn Any>>());
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//! ```
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//!
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//! ## Examples
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//!
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//! Consider a situation where we want to log a value passed to a function.
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//! We know the value we're working on implements `Debug`, but we don't know its
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//! concrete type. We want to give special treatment to certain types: in this
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//! case printing out the length of `String` values prior to their value.
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//! We don't know the concrete type of our value at compile time, so we need to
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//! use runtime reflection instead.
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//!
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//! ```rust
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//! use std::fmt::Debug;
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//! use std::any::Any;
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//!
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//! // Logger function for any type that implements `Debug`.
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//! fn log<T: Any + Debug>(value: &T) {
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//! let value_any = value as &dyn Any;
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//!
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//! // Try to convert our value to a `String`. If successful, we want to
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//! // output the `String`'s length as well as its value. If not, it's a
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//! // different type: just print it out unadorned.
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//! match value_any.downcast_ref::<String>() {
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//! Some(as_string) => {
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//! println!("String ({}): {}", as_string.len(), as_string);
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//! }
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//! None => {
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//! println!("{value:?}");
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//! }
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//! }
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//! }
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//!
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//! // This function wants to log its parameter out prior to doing work with it.
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//! fn do_work<T: Any + Debug>(value: &T) {
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//! log(value);
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//! // ...do some other work
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//! }
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//!
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//! fn main() {
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//! let my_string = "Hello World".to_string();
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//! do_work(&my_string);
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//!
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//! let my_i8: i8 = 100;
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//! do_work(&my_i8);
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//! }
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//! ```
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//!
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#![stable(feature = "rust1", since = "1.0.0")]
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use crate::fmt;
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use crate::hash;
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use crate::intrinsics;
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///////////////////////////////////////////////////////////////////////////////
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// Any trait
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///////////////////////////////////////////////////////////////////////////////
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/// A trait to emulate dynamic typing.
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///
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/// Most types implement `Any`. However, any type which contains a non-`'static` reference does not.
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/// See the [module-level documentation][mod] for more details.
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///
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/// [mod]: crate::any
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// This trait is not unsafe, though we rely on the specifics of it's sole impl's
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// `type_id` function in unsafe code (e.g., `downcast`). Normally, that would be
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// a problem, but because the only impl of `Any` is a blanket implementation, no
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// other code can implement `Any`.
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//
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// We could plausibly make this trait unsafe -- it would not cause breakage,
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// since we control all the implementations -- but we choose not to as that's
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// both not really necessary and may confuse users about the distinction of
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// unsafe traits and unsafe methods (i.e., `type_id` would still be safe to call,
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// but we would likely want to indicate as such in documentation).
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#[stable(feature = "rust1", since = "1.0.0")]
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#[cfg_attr(not(test), rustc_diagnostic_item = "Any")]
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pub trait Any: 'static {
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/// Gets the `TypeId` of `self`.
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///
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/// If called on a `dyn Any` trait object
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/// (or a trait object of a subtrait of `Any`),
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/// this returns the `TypeId` of the underlying
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/// concrete type, not that of `dyn Any` itself.
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///
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/// # Examples
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///
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/// ```
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/// use std::any::{Any, TypeId};
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///
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/// fn is_string(s: &dyn Any) -> bool {
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/// TypeId::of::<String>() == s.type_id()
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/// }
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///
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/// assert_eq!(is_string(&0), false);
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/// assert_eq!(is_string(&"cookie monster".to_string()), true);
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/// ```
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#[stable(feature = "get_type_id", since = "1.34.0")]
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fn type_id(&self) -> TypeId;
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: 'static + ?Sized> Any for T {
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fn type_id(&self) -> TypeId {
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TypeId::of::<T>()
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}
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}
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///////////////////////////////////////////////////////////////////////////////
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// Extension methods for Any trait objects.
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///////////////////////////////////////////////////////////////////////////////
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#[stable(feature = "rust1", since = "1.0.0")]
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impl fmt::Debug for dyn Any {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.debug_struct("Any").finish_non_exhaustive()
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}
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}
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// Ensure that the result of e.g., joining a thread can be printed and
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// hence used with `unwrap`. May eventually no longer be needed if
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// dispatch works with upcasting.
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#[stable(feature = "rust1", since = "1.0.0")]
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impl fmt::Debug for dyn Any + Send {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.debug_struct("Any").finish_non_exhaustive()
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}
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}
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#[stable(feature = "any_send_sync_methods", since = "1.28.0")]
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impl fmt::Debug for dyn Any + Send + Sync {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.debug_struct("Any").finish_non_exhaustive()
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}
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}
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impl dyn Any {
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/// Returns `true` if the inner type is the same as `T`.
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///
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/// # Examples
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///
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/// ```
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/// use std::any::Any;
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///
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/// fn is_string(s: &dyn Any) {
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/// if s.is::<String>() {
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/// println!("It's a string!");
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/// } else {
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/// println!("Not a string...");
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/// }
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/// }
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///
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/// is_string(&0);
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/// is_string(&"cookie monster".to_string());
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[inline]
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pub fn is<T: Any>(&self) -> bool {
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// Get `TypeId` of the type this function is instantiated with.
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let t = TypeId::of::<T>();
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// Get `TypeId` of the type in the trait object (`self`).
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let concrete = self.type_id();
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// Compare both `TypeId`s on equality.
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t == concrete
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}
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/// Returns some reference to the inner value if it is of type `T`, or
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/// `None` if it isn't.
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///
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/// # Examples
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///
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/// ```
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/// use std::any::Any;
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///
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/// fn print_if_string(s: &dyn Any) {
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/// if let Some(string) = s.downcast_ref::<String>() {
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/// println!("It's a string({}): '{}'", string.len(), string);
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/// } else {
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/// println!("Not a string...");
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/// }
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/// }
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///
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/// print_if_string(&0);
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/// print_if_string(&"cookie monster".to_string());
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[inline]
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pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
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if self.is::<T>() {
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// SAFETY: just checked whether we are pointing to the correct type, and we can rely on
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// that check for memory safety because we have implemented Any for all types; no other
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// impls can exist as they would conflict with our impl.
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unsafe { Some(self.downcast_ref_unchecked()) }
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} else {
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None
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}
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}
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/// Returns some mutable reference to the inner value if it is of type `T`, or
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/// `None` if it isn't.
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///
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/// # Examples
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///
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/// ```
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/// use std::any::Any;
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///
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/// fn modify_if_u32(s: &mut dyn Any) {
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/// if let Some(num) = s.downcast_mut::<u32>() {
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/// *num = 42;
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/// }
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/// }
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///
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/// let mut x = 10u32;
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/// let mut s = "starlord".to_string();
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///
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/// modify_if_u32(&mut x);
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/// modify_if_u32(&mut s);
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///
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/// assert_eq!(x, 42);
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/// assert_eq!(&s, "starlord");
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[inline]
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pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> {
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if self.is::<T>() {
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// SAFETY: just checked whether we are pointing to the correct type, and we can rely on
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// that check for memory safety because we have implemented Any for all types; no other
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// impls can exist as they would conflict with our impl.
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unsafe { Some(self.downcast_mut_unchecked()) }
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} else {
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None
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}
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}
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/// Returns a reference to the inner value as type `dyn T`.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(downcast_unchecked)]
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///
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/// use std::any::Any;
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///
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/// let x: Box<dyn Any> = Box::new(1_usize);
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///
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/// unsafe {
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/// assert_eq!(*x.downcast_ref_unchecked::<usize>(), 1);
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/// }
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/// ```
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///
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/// # Safety
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///
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/// The contained value must be of type `T`. Calling this method
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/// with the incorrect type is *undefined behavior*.
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#[unstable(feature = "downcast_unchecked", issue = "90850")]
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#[inline]
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pub unsafe fn downcast_ref_unchecked<T: Any>(&self) -> &T {
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debug_assert!(self.is::<T>());
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// SAFETY: caller guarantees that T is the correct type
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unsafe { &*(self as *const dyn Any as *const T) }
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}
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/// Returns a mutable reference to the inner value as type `dyn T`.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(downcast_unchecked)]
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///
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/// use std::any::Any;
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///
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/// let mut x: Box<dyn Any> = Box::new(1_usize);
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///
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/// unsafe {
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/// *x.downcast_mut_unchecked::<usize>() += 1;
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/// }
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///
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/// assert_eq!(*x.downcast_ref::<usize>().unwrap(), 2);
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/// ```
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///
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/// # Safety
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///
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/// The contained value must be of type `T`. Calling this method
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/// with the incorrect type is *undefined behavior*.
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#[unstable(feature = "downcast_unchecked", issue = "90850")]
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#[inline]
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pub unsafe fn downcast_mut_unchecked<T: Any>(&mut self) -> &mut T {
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debug_assert!(self.is::<T>());
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// SAFETY: caller guarantees that T is the correct type
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unsafe { &mut *(self as *mut dyn Any as *mut T) }
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}
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}
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impl dyn Any + Send {
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/// Forwards to the method defined on the type `dyn Any`.
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///
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/// # Examples
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///
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/// ```
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/// use std::any::Any;
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///
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/// fn is_string(s: &(dyn Any + Send)) {
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/// if s.is::<String>() {
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/// println!("It's a string!");
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/// } else {
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/// println!("Not a string...");
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/// }
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/// }
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///
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/// is_string(&0);
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/// is_string(&"cookie monster".to_string());
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[inline]
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pub fn is<T: Any>(&self) -> bool {
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<dyn Any>::is::<T>(self)
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}
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/// Forwards to the method defined on the type `dyn Any`.
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///
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/// # Examples
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///
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/// ```
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/// use std::any::Any;
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///
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/// fn print_if_string(s: &(dyn Any + Send)) {
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/// if let Some(string) = s.downcast_ref::<String>() {
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/// println!("It's a string({}): '{}'", string.len(), string);
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/// } else {
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/// println!("Not a string...");
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/// }
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/// }
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///
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/// print_if_string(&0);
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/// print_if_string(&"cookie monster".to_string());
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[inline]
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pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
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<dyn Any>::downcast_ref::<T>(self)
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}
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/// Forwards to the method defined on the type `dyn Any`.
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///
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/// # Examples
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///
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/// ```
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/// use std::any::Any;
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///
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/// fn modify_if_u32(s: &mut (dyn Any + Send)) {
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/// if let Some(num) = s.downcast_mut::<u32>() {
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/// *num = 42;
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/// }
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/// }
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///
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/// let mut x = 10u32;
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/// let mut s = "starlord".to_string();
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///
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/// modify_if_u32(&mut x);
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/// modify_if_u32(&mut s);
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///
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/// assert_eq!(x, 42);
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/// assert_eq!(&s, "starlord");
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[inline]
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pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> {
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<dyn Any>::downcast_mut::<T>(self)
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}
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/// Forwards to the method defined on the type `dyn Any`.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(downcast_unchecked)]
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///
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/// use std::any::Any;
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///
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/// let x: Box<dyn Any> = Box::new(1_usize);
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///
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/// unsafe {
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/// assert_eq!(*x.downcast_ref_unchecked::<usize>(), 1);
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/// }
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/// ```
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///
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/// # Safety
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///
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/// Same as the method on the type `dyn Any`.
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|
#[unstable(feature = "downcast_unchecked", issue = "90850")]
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#[inline]
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pub unsafe fn downcast_ref_unchecked<T: Any>(&self) -> &T {
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// SAFETY: guaranteed by caller
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unsafe { <dyn Any>::downcast_ref_unchecked::<T>(self) }
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}
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|
|
|
/// Forwards to the method defined on the type `dyn Any`.
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///
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|
/// # Examples
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|
///
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/// ```
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|
/// #![feature(downcast_unchecked)]
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///
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/// use std::any::Any;
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///
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/// let mut x: Box<dyn Any> = Box::new(1_usize);
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///
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/// unsafe {
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/// *x.downcast_mut_unchecked::<usize>() += 1;
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/// }
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///
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/// assert_eq!(*x.downcast_ref::<usize>().unwrap(), 2);
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/// ```
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///
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/// # Safety
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///
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/// Same as the method on the type `dyn Any`.
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|
#[unstable(feature = "downcast_unchecked", issue = "90850")]
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|
#[inline]
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pub unsafe fn downcast_mut_unchecked<T: Any>(&mut self) -> &mut T {
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// SAFETY: guaranteed by caller
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unsafe { <dyn Any>::downcast_mut_unchecked::<T>(self) }
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}
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}
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impl dyn Any + Send + Sync {
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/// Forwards to the method defined on the type `Any`.
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///
|
|
/// # Examples
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|
///
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/// ```
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/// use std::any::Any;
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///
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/// fn is_string(s: &(dyn Any + Send + Sync)) {
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/// if s.is::<String>() {
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/// println!("It's a string!");
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/// } else {
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|
/// println!("Not a string...");
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/// }
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/// }
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///
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/// is_string(&0);
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/// is_string(&"cookie monster".to_string());
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/// ```
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|
#[stable(feature = "any_send_sync_methods", since = "1.28.0")]
|
|
#[inline]
|
|
pub fn is<T: Any>(&self) -> bool {
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|
<dyn Any>::is::<T>(self)
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|
}
|
|
|
|
/// Forwards to the method defined on the type `Any`.
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|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
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|
/// use std::any::Any;
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|
///
|
|
/// fn print_if_string(s: &(dyn Any + Send + Sync)) {
|
|
/// if let Some(string) = s.downcast_ref::<String>() {
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|
/// println!("It's a string({}): '{}'", string.len(), string);
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|
/// } else {
|
|
/// println!("Not a string...");
|
|
/// }
|
|
/// }
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|
///
|
|
/// 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, Debug, Eq, PartialOrd, Ord)]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
pub struct TypeId {
|
|
// We avoid using `u128` because that imposes higher alignment requirements on many platforms.
|
|
// See issue #115620 for more information.
|
|
t: (u64, u64),
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl PartialEq for TypeId {
|
|
#[inline]
|
|
fn eq(&self, other: &Self) -> bool {
|
|
self.t == other.t
|
|
}
|
|
}
|
|
|
|
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 {
|
|
let t: u128 = intrinsics::type_id::<T>();
|
|
|
|
let t1 = (t >> 64) as u64;
|
|
let t2 = t as u64;
|
|
TypeId { t: (t1, t2) }
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl hash::Hash for TypeId {
|
|
#[inline]
|
|
fn hash<H: hash::Hasher>(&self, state: &mut H) {
|
|
// We only hash the lower 64 bits of our (128 bit) internal numeric ID,
|
|
// because:
|
|
// - The hashing algorithm which backs `TypeId` is expected to be
|
|
// unbiased and high quality, meaning further mixing would be somewhat
|
|
// redundant compared to choosing (the lower) 64 bits arbitrarily.
|
|
// - `Hasher::finish` returns a u64 anyway, so the extra entropy we'd
|
|
// get from hashing the full value would probably not be useful
|
|
// (especially given the previous point about the lower 64 bits being
|
|
// high quality on their own).
|
|
// - It is correct to do so -- only hashing a subset of `self` is still
|
|
// with an `Eq` implementation that considers the entire value, as
|
|
// ours does.
|
|
self.t.1.hash(state);
|
|
}
|
|
}
|
|
|
|
/// 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 type name 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
|
|
///
|
|
/// Like [`type_name`], this is intended for diagnostic use and the exact output is not
|
|
/// guaranteed. It provides a best-effort description, but the output may change between
|
|
/// versions of the compiler.
|
|
///
|
|
/// In short: use this for debugging, avoid using the output to affect program behavior. More
|
|
/// information is available at [`type_name`].
|
|
///
|
|
/// Additionally, this function does not resolve trait objects. This means that
|
|
/// `type_name_of_val(&7u32 as &dyn Debug)` may return `"dyn Debug"`, but will not return `"u32"`
|
|
/// at this time.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Prints the default integer and float types.
|
|
///
|
|
/// ```rust
|
|
/// use std::any::type_name_of_val;
|
|
///
|
|
/// let s = "foo";
|
|
/// let x: i32 = 1;
|
|
/// let y: f32 = 1.0;
|
|
///
|
|
/// assert!(type_name_of_val(&s).contains("str"));
|
|
/// assert!(type_name_of_val(&x).contains("i32"));
|
|
/// assert!(type_name_of_val(&y).contains("f32"));
|
|
/// ```
|
|
#[must_use]
|
|
#[stable(feature = "type_name_of_val", since = "1.76.0")]
|
|
#[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>()
|
|
}
|