Introduction

Here's how to use a Python-like range in Rust.

It can be used as follows.

// for i in range(5):
//     print(i)
for i in range!(5) {
    println!("{}", i);
}

// for i in range(1, 5):
//     print(i)
for i in range!(1, 5) {
    println!("{}", i);
}

// for i in range(1, 5, 2):
//     print(i)
for i in range!(1, 5, 2) {
    println!("{}", i);
}

// for i in range(5, 1, -1):
//     print(i)
for i in range!(5, 1, -1) {
    println!("{}", i);
}

manner

You can implement a Python-like range with the following macros.

macro_rules! range {
    ($stop:expr) => {
        0..$stop
    };
    ($start:expr, $stop:expr) => {
        $start..$stop
    };
    ($start:expr, $stop:expr, -$step:expr) => {
        ($stop + 1..$start + 1).rev().step_by($step)
    };
    ($start:expr, $stop:expr, $step:expr) => {
        ($start..$stop).step_by($step)
    };
}

It basically returns the same iterator as the Python range function.

Things impossible

When specifying a negative step, step_by () can only receive ʻusize, so you need to reverse the iterator with rev () . Therefore, the presence or absence of - is judged by pattern matching, and it is decided whether to perform rev () `. Therefore, if a variable contains a negative number and is given as a step, it cannot be determined as a negative number by pattern matching, resulting in a compile error.

//Compile error
let x = -1;
for i in range!(5, 1, x) {
    println!("{}", i);
}

I would like to know if there is a way to implement this well.

Finally

Rust macros have a lot of freedom, so it's a lot of fun.

Use Python-like range with Rust

Introduction

manner

Things impossible

Finally