Primitive Type bool

The boolean type.

The bool represents a value, which could only be either true or false. If you cast a bool into an integer, true will be 1 and false will be 0.

Basic usage

bool implements various traits, such as BitAnd, BitOr, Not, etc., which allow us to perform boolean operations using &, | and !.

if requires a bool value as its conditional. assert!, which is an important macro in testing, checks whether an expression is true and panics if it isn’t.

let bool_val = true & false | false;
assert!(!bool_val);

Examples

A trivial example of the usage of bool:

let praise_the_borrow_checker = true;

// using the `if` conditional
if praise_the_borrow_checker {
    println!("oh, yeah!");
} else {
    println!("what?!!");
}

// ... or, a match pattern
match praise_the_borrow_checker {
    true => println!("keep praising!"),
    false => println!("you should praise!"),
}

Also, since bool implements the Copy trait, we don’t have to worry about the move semantics (just like the integer and float primitives).

Now an example of bool cast to integer type:

assert_eq!(true as i32, 1);
assert_eq!(false as i32, 0);

Implementations

impl bool

pub fn then_some<T>(self, t: T) -> Option<T>

Returns Some(t) if the bool is true, or None otherwise.

Arguments passed to then_some are eagerly evaluated; if you are passing the result of a function call, it is recommended to use then, which is lazily evaluated.

Examples

assert_eq!(false.then_some(0), None);
assert_eq!(true.then_some(0), Some(0));

let mut a = 0;
let mut function_with_side_effects = || { a  = 1; };

true.then_some(function_with_side_effects());
false.then_some(function_with_side_effects());

// `a` is incremented twice because the value passed to `then_some` is
// evaluated eagerly.
assert_eq!(a, 2);

pub fn then<T, F>(self, f: F) -> Option<T>

where F: FnOnce() -> T,

Returns Some(f()) if the bool is true, or None otherwise.

Examples

assert_eq!(false.then(|| 0), None);
assert_eq!(true.then(|| 0), Some(0));

let mut a = 0;

true.then(|| { a  = 1; });
false.then(|| { a  = 1; });

// `a` is incremented once because the closure is evaluated lazily by
// `then`.
assert_eq!(a, 1);

pub fn select_unpredictable<T>(self, true_val: T, false_val: T) -> T

🔬This is a nightly-only experimental API. (select_unpredictable #133962)

Returns either true_val or false_val depending on the value of self, with a hint to the compiler that self is unlikely to be correctly predicted by a CPU’s branch predictor.

This method is functionally equivalent to

fn select_unpredictable<T>(b: bool, true_val: T, false_val: T) -> T {
    if b { true_val } else { false_val }
}

but might generate different assembly. In particular, on platforms with a conditional move or select instruction (like cmov on x86 or csel on ARM) the optimizer might use these instructions to avoid branches, which can benefit performance if the branch predictor is struggling with predicting condition, such as in an implementation of binary search.

Note however that this lowering is not guaranteed (on any platform) and should not be relied upon when trying to write constant-time code. Also be aware that this lowering might decrease performance if condition is well-predictable. It is advisable to perform benchmarks to tell if this function is useful.

Examples

Distribute values evenly between two buckets:

#![feature(select_unpredictable)]

use std::hash::BuildHasher;

fn append<H: BuildHasher>(hasher: &H, v: i32, bucket_one: &mut Vec<i32>, bucket_two: &mut Vec<i32>) {
    let hash = hasher.hash_one(&v);
    let bucket = (hash % 2 == 0).select_unpredictable(bucket_one, bucket_two);
    bucket.push(v);
}

Trait Implementations

impl BitAnd<&bool> for &bool

type Output = <bool as BitAnd>::Output

The resulting type after applying the & operator.

fn bitand(self, other: &bool) -> <bool as BitAnd>::Output

Performs the & operation.

impl BitAnd<&bool> for bool

type Output = <bool as BitAnd>::Output

The resulting type after applying the & operator.

fn bitand(self, other: &bool) -> <bool as BitAnd>::Output

Performs the & operation.

impl<T, const N: usize> BitAnd<Mask<T, N>> for bool

where T: MaskElement, LaneCount<N>: SupportedLaneCount,

type Output = Mask<T, N>

The resulting type after applying the & operator.

fn bitand(self, rhs: Mask<T, N>) -> Mask<T, N>

Performs the & operation.

impl<'a> BitAnd<bool> for &'a bool

type Output = <bool as BitAnd>::Output

The resulting type after applying the & operator.

fn bitand(self, other: bool) -> <bool as BitAnd>::Output

Performs the & operation.

impl<T, const N: usize> BitAnd<bool> for Mask<T, N>

where T: MaskElement, LaneCount<N>: SupportedLaneCount,

type Output = Mask<T, N>

The resulting type after applying the & operator.

fn bitand(self, rhs: bool) -> Mask<T, N>

Performs the & operation.

impl BitAnd for bool

type Output = bool

The resulting type after applying the & operator.

fn bitand(self, rhs: bool) -> bool

Performs the & operation.

impl BitAndAssign<&bool> for bool

fn bitand_assign(&mut self, other: &bool)

Performs the &= operation.

impl<T, const N: usize> BitAndAssign<bool> for Mask<T, N>

where T: MaskElement, LaneCount<N>: SupportedLaneCount,

fn bitand_assign(&mut self, rhs: bool)

Performs the &= operation.

impl BitAndAssign for bool

fn bitand_assign(&mut self, other: bool)

Performs the &= operation.

impl BitOr<&bool> for &bool

type Output = <bool as BitOr>::Output

The resulting type after applying the | operator.

fn bitor(self, other: &bool) -> <bool as BitOr>::Output

Performs the | operation.

impl BitOr<&bool> for bool

type Output = <bool as BitOr>::Output

The resulting type after applying the | operator.

fn bitor(self, other: &bool) -> <bool as BitOr>::Output

Performs the | operation.

impl<T, const N: usize> BitOr<Mask<T, N>> for bool

where T: MaskElement, LaneCount<N>: SupportedLaneCount,

type Output = Mask<T, N>

The resulting type after applying the | operator.

fn bitor(self, rhs: Mask<T, N>) -> Mask<T, N>

Performs the | operation.

impl<'a> BitOr<bool> for &'a bool

type Output = <bool as BitOr>::Output

The resulting type after applying the | operator.

fn bitor(self, other: bool) -> <bool as BitOr>::Output

Performs the | operation.

impl<T, const N: usize> BitOr<bool> for Mask<T, N>

where T: MaskElement, LaneCount<N>: SupportedLaneCount,

type Output = Mask<T, N>

The resulting type after applying the | operator.

fn bitor(self, rhs: bool) -> Mask<T, N>

Performs the | operation.

impl BitOr for bool

type Output = bool

The resulting type after applying the | operator.

fn bitor(self, rhs: bool) -> bool

Performs the | operation.

impl BitOrAssign<&bool> for bool

fn bitor_assign(&mut self, other: &bool)

Performs the |= operation.

impl<T, const N: usize> BitOrAssign<bool> for Mask<T, N>

where T: MaskElement, LaneCount<N>: SupportedLaneCount,

fn bitor_assign(&mut self, rhs: bool)

Performs the |= operation.

impl BitOrAssign for bool

fn bitor_assign(&mut self, other: bool)

Performs the |= operation.

impl BitXor<&bool> for &bool

type Output = <bool as BitXor>::Output

The resulting type after applying the ^ operator.

fn bitxor(self, other: &bool) -> <bool as BitXor>::Output

Performs the ^ operation.

impl BitXor<&bool> for bool

type Output = <bool as BitXor>::Output

The resulting type after applying the ^ operator.

fn bitxor(self, other: &bool) -> <bool as BitXor>::Output

Performs the ^ operation.

impl<T, const N: usize> BitXor<Mask<T, N>> for bool

where T: MaskElement, LaneCount<N>: SupportedLaneCount,

type Output = Mask<T, N>

The resulting type after applying the ^ operator.

fn bitxor(self, rhs: Mask<T, N>) -> <bool as BitXor<Mask<T, N>>>::Output

Performs the ^ operation.

impl<'a> BitXor<bool> for &'a bool

type Output = <bool as BitXor>::Output

The resulting type after applying the ^ operator.

fn bitxor(self, other: bool) -> <bool as BitXor>::Output

Performs the ^ operation.

impl<T, const N: usize> BitXor<bool> for Mask<T, N>

where T: MaskElement, LaneCount<N>: SupportedLaneCount,

type Output = Mask<T, N>

The resulting type after applying the ^ operator.

fn bitxor(self, rhs: bool) -> <Mask<T, N> as BitXor<bool>>::Output

Performs the ^ operation.

impl BitXor for bool

type Output = bool

The resulting type after applying the ^ operator.

fn bitxor(self, other: bool) -> bool

Performs the ^ operation.

impl BitXorAssign<&bool> for bool

fn bitxor_assign(&mut self, other: &bool)

Performs the ^= operation.

impl<T, const N: usize> BitXorAssign<bool> for Mask<T, N>

where T: MaskElement, LaneCount<N>: SupportedLaneCount,

fn bitxor_assign(&mut self, rhs: bool)

Performs the ^= operation.

impl BitXorAssign for bool

fn bitxor_assign(&mut self, other: bool)

Performs the ^= operation.

impl Clone for bool

fn clone(&self) -> bool

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for bool

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

Formats the value using the given formatter.

impl Default for bool

fn default() -> bool

Returns the default value of false

impl Display for bool

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

Formats the value using the given formatter.

impl From<bool> for AtomicBool

fn from(b: bool) -> AtomicBool

Converts a bool into an AtomicBool.

Examples

use std::sync::atomic::AtomicBool;
let atomic_bool = AtomicBool::from(true);
assert_eq!(format!("{atomic_bool:?}"), "true")

impl From<bool> for f32

fn from(small: bool) -> f32

Converts a bool to f32 losslessly. The resulting value is positive 0.0 for false and 1.0 for true values.

Examples

let x: f32 = false.into();
assert_eq!(x, 0.0);
assert!(x.is_sign_positive());

let y: f32 = true.into();
assert_eq!(y, 1.0);

impl From<bool> for f64

fn from(small: bool) -> f64

Converts a bool to f64 losslessly. The resulting value is positive 0.0 for false and 1.0 for true values.

Examples

let x: f64 = false.into();
assert_eq!(x, 0.0);
assert!(x.is_sign_positive());

let y: f64 = true.into();
assert_eq!(y, 1.0);

impl From<bool> for i128

fn from(small: bool) -> i128

Converts a bool to i128 losslessly. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(i128::from(true), 1);
assert_eq!(i128::from(false), 0);

impl From<bool> for i16

fn from(small: bool) -> i16

Converts a bool to i16 losslessly. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(i16::from(true), 1);
assert_eq!(i16::from(false), 0);

impl From<bool> for i32

fn from(small: bool) -> i32

Converts a bool to i32 losslessly. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(i32::from(true), 1);
assert_eq!(i32::from(false), 0);

impl From<bool> for i64

fn from(small: bool) -> i64

Converts a bool to i64 losslessly. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(i64::from(true), 1);
assert_eq!(i64::from(false), 0);

impl From<bool> for i8

fn from(small: bool) -> i8

Converts a bool to i8 losslessly. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(i8::from(true), 1);
assert_eq!(i8::from(false), 0);

impl From<bool> for isize

fn from(small: bool) -> isize

Converts a bool to isize losslessly. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(isize::from(true), 1);
assert_eq!(isize::from(false), 0);

impl From<bool> for u128

fn from(small: bool) -> u128

Converts a bool to u128 losslessly. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(u128::from(true), 1);
assert_eq!(u128::from(false), 0);

impl From<bool> for u16

fn from(small: bool) -> u16

Converts a bool to u16 losslessly. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(u16::from(true), 1);
assert_eq!(u16::from(false), 0);

impl From<bool> for u32

fn from(small: bool) -> u32

Converts a bool to u32 losslessly. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(u32::from(true), 1);
assert_eq!(u32::from(false), 0);

impl From<bool> for u64

fn from(small: bool) -> u64

Converts a bool to u64 losslessly. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(u64::from(true), 1);
assert_eq!(u64::from(false), 0);

impl From<bool> for u8

fn from(small: bool) -> u8

Converts a bool to u8 losslessly. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(u8::from(true), 1);
assert_eq!(u8::from(false), 0);

impl From<bool> for usize

fn from(small: bool) -> usize

Converts a bool to usize losslessly. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(usize::from(true), 1);
assert_eq!(usize::from(false), 0);

impl FromStr for bool

fn from_str(s: &str) -> Result<bool, ParseBoolError>

Parse a bool from a string.

The only accepted values are "true" and "false". Any other input will return an error.

Examples

use std::str::FromStr;

assert_eq!(FromStr::from_str("true"), Ok(true));
assert_eq!(FromStr::from_str("false"), Ok(false));
assert!(<bool as FromStr>::from_str("not even a boolean").is_err());

Note, in many cases, the .parse() method on str is more proper.

assert_eq!("true".parse(), Ok(true));
assert_eq!("false".parse(), Ok(false));
assert!("not even a boolean".parse::<bool>().is_err());

type Err = ParseBoolError

The associated error which can be returned from parsing.

impl Hash for bool

fn hash<H>(&self, state: &mut H)

where H: Hasher,

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Not for &bool

type Output = <bool as Not>::Output

The resulting type after applying the ! operator.

fn not(self) -> <bool as Not>::Output

Performs the unary ! operation.

impl Not for bool

type Output = bool

The resulting type after applying the ! operator.

fn not(self) -> bool

Performs the unary ! operation.

impl Ord for bool

fn cmp(&self, other: &bool) -> Ordering

This method returns an Ordering between self and other.

fn min(self, other: bool) -> bool

Compares and returns the minimum of two values.

fn max(self, other: bool) -> bool

Compares and returns the maximum of two values.

fn clamp(self, min: bool, max: bool) -> bool

Restrict a value to a certain interval.

impl PartialEq for bool

fn eq(&self, other: &bool) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &bool) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl PartialOrd for bool

fn partial_cmp(&self, other: &bool) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl Random for bool

fn random(source: &mut (impl RandomSource ?Sized)) -> bool

🔬This is a nightly-only experimental API. (random #130703)

Generates a random value.

impl ConstParamTy_ for bool

impl Copy for bool

impl Eq for bool

impl StructuralPartialEq for bool

impl UnsizedConstParamTy for bool