# Trait std::any::Any

1.0.0 · source ·

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

Expand description

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§

1.34.0 · source

#### 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);

Run

## Implementations§

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### impl<A> Box<dyn Any, A>where A: Allocator,

source

#### pub fn downcast<T>(self) -> Result<Box<T, A>, Box<dyn Any, 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));

Run
source

#### 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);
    }

Run

##### Safety

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

source§

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

source

#### pub fn downcast<T>(self) -> Result<Box<T, A>, Box<dyn Any + Send, 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));

Run
source

#### 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);
    }

Run

##### Safety

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

source§

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

1.51.0 · source

#### pub fn downcast<T>(self) -> Result<Box<T, A>, Box<dyn Any + Send + Sync, 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));

Run
source

#### 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);
    }

Run

##### Safety

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

source§

### impl dyn Any

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#### pub fn is<T>(&self) -> bool where 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());

Run
source

#### 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());

Run
source

#### 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");

Run
source

#### pub unsafe fn downcast_ref_unchecked<T>(&self) -> &T where 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);
    }

Run

##### Safety

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

source

#### pub unsafe fn downcast_mut_unchecked<T>(&mut self) -> &mut T where 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);

Run

##### Safety

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

source§

### impl dyn Any + Send

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#### pub fn is<T>(&self) -> bool where 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());

Run
source

#### 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());

Run
source

#### 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");

Run
source

#### pub unsafe fn downcast_ref_unchecked<T>(&self) -> &T where 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);
    }

Run

##### Safety

Same as the method on the type `dyn Any`.

source

#### pub unsafe fn downcast_mut_unchecked<T>(&mut self) -> &mut T where 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);

Run

##### Safety

Same as the method on the type `dyn Any`.

source§

### impl dyn Any + Send + Sync

1.28.0 · source

#### pub fn is<T>(&self) -> bool where 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());

Run
1.28.0 · source

#### 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());

Run
1.28.0 · source

#### 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");

Run
source

#### pub unsafe fn downcast_ref_unchecked<T>(&self) -> &T where 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);
    }

Run
source

#### pub unsafe fn downcast_mut_unchecked<T>(&mut self) -> &mut T where 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);

Run

## Trait Implementations§

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### impl Debug for dyn Any

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

Formats the value using the given formatter. Read more
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### impl Debug for dyn Any + Send

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

Formats the value using the given formatter. Read more
1.28.0 · source§

### impl Debug for dyn Any + Send + Sync

source§

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

Formats the value using the given formatter. Read more

## Implementors§

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