6.3 Booleans

The boolean type is represented by the bool keyword and accepts the values true and false:

let a = true;
let b = false;
(a, b)

6.3.1Logical operators¶

Logical operators (see Table 1) combine boolean values to give a new boolean value.

The NOT operator ! negates the value:

// don't remove the initial white space 
 ! false

The AND operator is represented by &:

(false & true, true & true)

The OR operator is represented by |:

false | true

The XOR operator is represented by ^:

(false ^ true, true ^ true)

6.3.1.1Short-circuiting operators¶

When combining boolean functions with the AND or OR operator, all functions are always evaluated.

Here are three boolean functions that we will use for demonstrating the way the operators work:

:clear

fn foo1() -> bool {
  println!("foo1()");
  true
}

fn foo2() -> bool {
  println!("foo2()");
  false
}

fn foo3() -> bool {
  println!("foo3()");
  true
}

Doing an OR operation between them results in the calling of the three function, despise the fact that he first function foo1() returns true:

let b = foo1() | foo2() | foo3();
println!("{b}");

foo1()

foo2()

foo3()

true

Similarly, an AND operation between the same functions triggers the calling of the three functions while the second one returns false:

let b = foo1() & foo2() & foo3();
println!("{b}");

foo1()

foo2()

foo3()

false

To avoid this side effect that can affect performance, two other operators are available. They are called short-circuiting operators:

• || is the short-circuiting OR.

• && is the short-circuiting AND.

Using the || operator, we that only the first function is evaluated:

let b = foo1() || foo2() || foo3();
println!("{b}");

foo1()

true

With the && operator, the last function is not evaluated:

let b = foo1() && foo2() && foo3();
println!("{b}");

foo1()

foo2()

false

6.3.2Comparison operators¶

Comparison operators (see Table 2) compare values of various types and return a boolean value.

The equality operator returns true if two values are equal:

(12.2 == 12.3, "abc" == "abc")

The less than operator return true if one value is strictly smaller than another:

(12.2 < 12.3, "abc" < "abc", "abc" < "abd")

Other operators are != (inequality), <=, > and >=.