What’s new in Rust 1.46.0 about const_fn?

Hello, folks! your wait is over, we have come up with a new blog. In this blog, we will discuss the new update about const_fn in the Rust update 1.46.0. I hope you will enjoy the blog.

Improvement in Const Function

The const_fn feature allows marking free functions and inherent methods as const, enabling them to be called in constants contexts, with constant arguments.

Example:

const fn square(x: i32) -> i32 {
    x * 2
}

const DIGIT: i32 = 10;
const RESULT: i32 = square(DIGIT);

fn main() {
    println!("The result of const function: {}",RESULT);
}

Output:

The result of const function: 20

So the new Rust stable release 1.46.0 enables quite a lot of new things to appear in const_fn, two new standard library APIs.

1. Use of if, if let, and match:

Now we can use the if, if let, and match in the const function which help to use conditions in the const function.

Example: .

// Use of if statement in const function.
const fn even(number: i32) -> i32 {
    if number %2 == 0 {
        number
    } else {
        number + 1
    }
}

// Use of match statement in const function.
const fn even_no (number: i32) -> i32 {
    match number {
        2 => number,
        _ => number + 1 ,
    }
}

const DIGIT: i32 = 9;
const RESULT: i32 = even(DIGIT);
const RESULT_MATCH: i32 = even_no(DIGIT);

fn main() {
    println!("The result of const function with if statement: {}", RESULT);
    println!("The result of const function with match statement: {}", RESULT_MATCH);
}

Output:

The result of const function with if statement: 10
The result of const function with match statement: 10

2. Use of while, while let, and loop:

After this release we can also use the while, while let, and loop in the const function which help to use loops in the const function.

Example:

// Use of while loop in const function.
const fn difference(mut number: i32) -> i32 {
    let mut counter = 0;
    while number <= 12 {
        counter = counter + 1;
        number = number +1;
    }
    counter
}

// Use of loop in const function.
const fn loop_fn (number: i32) -> i32 {
    loop {
         if number == 9  
            {
            break;
       }
    }
    number
}

const DIGIT: i32 = 9;
const RESULT: i32 = difference(DIGIT);
const RESULT2: i32 = loop_fn(DIGIT);

fn main() {
    println!("The result of const function with while loop: {}", RESULT);
    println!("The result of const function with loop: {}", RESULT2);
}

Output:

The result of const function with while loop: 4
The result of const function with loop: 9

3. Use of && and || operators:

This release enables the && and || operators in the const function which help to use operators in the const function.

Example:

// Use of && and || operators in const function.
const fn operators(number: i32) -> i32 {
    if number >= 5 && number <=10 {
        if number == 8 || number == 9 {
            number
        } else {
        0
      }
    } else {
        0
      }
}

const DIGIT: i32 = 9;
const RESULT: i32 = operators(DIGIT);

fn main() {
    println!("The result of const function with operators: {}", RESULT);
}

Output:

The result of const function with operators: 9

Note: I hope our blogs help you to enhance your learning. I’ll post more blogs on Rust. Stay Tuned.

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