Macro tear::tear_if

macro_rules! tear_if {
    ( $c:expr $( , $($b:tt)* )? ) => { ... };
    ( let $p:pat = $e:expr $( , $($b:tt)* )? ) => { ... };
}

Explicit if statement with early return

Description

tear_if! { cond,  // <- NB: it's a comma
    do_things();
    v             // Return value
}

If cond is true, it executes the statements in its body and returns its value (v here). It’s basically an early return without the return statement at the end.

tear_if! { let pat = expr,
    do_things();
    v
}

You can also use the pattern matching if let.

Examples

Early return a value: recursively computing the length of a slice.

fn len (v: &[i32]) -> usize {
    // Base case
    tear_if! { v.is_empty(), 0 as usize }
    
    // Recursion
    1 + len(&v[1..])
}

Handle simple cases: printing help in a command line utility

use std::env;

fn main() {
    let args: Vec<String> = env::args().collect();
    tear_if! { args.contains(&String::from("--help")),
        println!("No help available.")
    }
    
    println!("Greetings, human!");
}

Use patterns like if let

fn add_five(x: Option<i32>) -> i32 {
    tear_if! { let None = x, 0 }
    
    x.unwrap() + 5
}

assert_eq![ add_five(Some(2)), 7 ];
assert_eq![ add_five(None), 0 ];