Macro if_return 

macro_rules! if_return {
    {
        $condition:expr $(=> $return_value:expr)?
    } => { ... };
    {
        $($condition:expr $(=> $return_value:expr)?)*
    } => { ... };
}

简化「if 条件 {return 值;}」的控制流

• 📄形式：if_return![a == 1 => 2] => if a == 1 {return 2;}

Examples

use nar_dev_utils::if_return;
fn starts_at(text: &str, prefix: &str) -> Option<usize> {
    // 截断式返回示例：多分支
    if_return! {
       prefix.is_empty() => Some(0)
       text.starts_with(prefix) => Some(0)
    }

    let mut i = 0;
    let max_i = text.len() - prefix.len();
    while i <= max_i {
        // 截断式返回示例：单分支 | 三行变一行
        if_return! { prefix == &text[i..(i + prefix.len())] => Some(i) }
        i += 1;
    }

    None
}

assert_eq!(starts_at("hello", ""), Some(0));
assert_eq!(starts_at("hello", "llo"), Some(2));
assert_eq!(starts_at("hello", "help"), None);

use nar_dev_utils::if_return;
fn raise_the_bar(num: usize, bar: &mut usize) {
    #![allow(clippy::unused_unit)]
    *bar = 0;
    // 截断式返回示例：隐式指定返回值（单元类型`()`）
    if_return! { num <= *bar }
    println!("{num} is greater than {bar}");

    *bar = 1;
    // 截断式返回示例：上述「隐式返回」与此处「显式返回」等价
    if_return! { num <= *bar => () }
    println!("{num} is greater than {bar}");
    *bar = 2;
}

let mut num = 0;
let mut bar = 0;
raise_the_bar(num, &mut bar);
assert_eq!(bar, 0);

num = 1;
raise_the_bar(num, &mut bar);
assert_eq!(bar, 1);

num = 2;
raise_the_bar(num, &mut bar);
assert_eq!(bar, 2);