Trait std::any::Any

pub trait Any: 'static {
    fn type_id(&self) -> TypeId;
}

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 for more details.

Required Methods

fn type_id(&self) -> TypeId

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);

Implementations

impl<A> Box<dyn Any + 'static, A>where
    A: Allocator,

pub fn downcast<T>(self) -> Result<Box<T, A>, Box<dyn Any + 'static, A>>where
    T: Any,

Attempt to downcast the box to a concrete type.

Examples

use std::any::Any;

fn print_if_string(value: Box<dyn Any>) {
    if let Ok(string) = value.downcast::<String>() {
        println!("String ({}): {}", string.len(), string);
    }
}

let my_string = "Hello World".to_string();
print_if_string(Box::new(my_string));
print_if_string(Box::new(0i8));

pub unsafe fn downcast_unchecked<T>(self) -> Box<T, A>where
    T: Any,

🔬This is a nightly-only experimental API. (downcast_unchecked #90850)

Downcasts the box to a concrete type.

For a safe alternative see downcast.

Examples

#![feature(downcast_unchecked)]

use std::any::Any;

let x: Box<dyn Any> = Box::new(1_usize);

unsafe {
    assert_eq!(*x.downcast_unchecked::<usize>(), 1);
}

Safety

The contained value must be of type T. Calling this method with the incorrect type is undefined behavior.

impl<A> Box<dyn Any + Send + 'static, A>where
    A: Allocator,

pub fn downcast<T>(self) -> Result<Box<T, A>, Box<dyn Any + Send + 'static, A>>where
    T: Any,

Attempt to downcast the box to a concrete type.

Examples

use std::any::Any;

fn print_if_string(value: Box<dyn Any + Send>) {
    if let Ok(string) = value.downcast::<String>() {
        println!("String ({}): {}", string.len(), string);
    }
}

let my_string = "Hello World".to_string();
print_if_string(Box::new(my_string));
print_if_string(Box::new(0i8));

pub unsafe fn downcast_unchecked<T>(self) -> Box<T, A>where
    T: Any,

🔬This is a nightly-only experimental API. (downcast_unchecked #90850)

Downcasts the box to a concrete type.

For a safe alternative see downcast.

Examples

#![feature(downcast_unchecked)]

use std::any::Any;

let x: Box<dyn Any + Send> = Box::new(1_usize);

unsafe {
    assert_eq!(*x.downcast_unchecked::<usize>(), 1);
}

Safety

The contained value must be of type T. Calling this method with the incorrect type is undefined behavior.

impl<A> Box<dyn Any + Send + Sync + 'static, A>where
    A: Allocator,

pub fn downcast<T>(
    self
) -> Result<Box<T, A>, Box<dyn Any + Send + Sync + 'static, A>>where
    T: Any,

Attempt to downcast the box to a concrete type.

Examples

use std::any::Any;

fn print_if_string(value: Box<dyn Any + Send + Sync>) {
    if let Ok(string) = value.downcast::<String>() {
        println!("String ({}): {}", string.len(), string);
    }
}

let my_string = "Hello World".to_string();
print_if_string(Box::new(my_string));
print_if_string(Box::new(0i8));

pub unsafe fn downcast_unchecked<T>(self) -> Box<T, A>where
    T: Any,

🔬This is a nightly-only experimental API. (downcast_unchecked #90850)

Downcasts the box to a concrete type.

For a safe alternative see downcast.

Examples

#![feature(downcast_unchecked)]

use std::any::Any;

let x: Box<dyn Any + Send + Sync> = Box::new(1_usize);

unsafe {
    assert_eq!(*x.downcast_unchecked::<usize>(), 1);
}

Safety

The contained value must be of type T. Calling this method with the incorrect type is undefined behavior.

impl dyn Any + 'static

pub fn is<T>(&self) -> boolwhere
    T: 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());

pub fn downcast_ref<T>(&self) -> Option<&T>where
    T: Any,

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());

pub fn downcast_mut<T>(&mut self) -> Option<&mut T>where
    T: Any,

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");

pub unsafe fn downcast_ref_unchecked<T>(&self) -> &Twhere
    T: Any,

🔬This is a nightly-only experimental API. (downcast_unchecked #90850)

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.

pub unsafe fn downcast_mut_unchecked<T>(&mut self) -> &mut Twhere
    T: Any,

🔬This is a nightly-only experimental API. (downcast_unchecked #90850)

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.

impl dyn Any + Send + 'static

pub fn is<T>(&self) -> boolwhere
    T: Any,

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());

pub fn downcast_ref<T>(&self) -> Option<&T>where
    T: Any,

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());

pub fn downcast_mut<T>(&mut self) -> Option<&mut T>where
    T: Any,

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");

pub unsafe fn downcast_ref_unchecked<T>(&self) -> &Twhere
    T: Any,

🔬This is a nightly-only experimental API. (downcast_unchecked #90850)

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.

pub unsafe fn downcast_mut_unchecked<T>(&mut self) -> &mut Twhere
    T: Any,

🔬This is a nightly-only experimental API. (downcast_unchecked #90850)

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.

impl dyn Any + Send + Sync + 'static

pub fn is<T>(&self) -> boolwhere
    T: Any,

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());

pub fn downcast_ref<T>(&self) -> Option<&T>where
    T: Any,

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());

pub fn downcast_mut<T>(&mut self) -> Option<&mut T>where
    T: Any,

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");

pub unsafe fn downcast_ref_unchecked<T>(&self) -> &Twhere
    T: Any,

🔬This is a nightly-only experimental API. (downcast_unchecked #90850)

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);
}

pub unsafe fn downcast_mut_unchecked<T>(&mut self) -> &mut Twhere
    T: Any,

🔬This is a nightly-only experimental API. (downcast_unchecked #90850)

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);

Trait Implementations

impl Debug for dyn Any + 'static

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Debug for dyn Any + Send + 'static

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Debug for dyn Any + Send + Sync + 'static

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

Implementors

impl<T> Any for Twhere
    T: 'static + ?Sized,