Macro if_match

macro_rules! if_match {
    ($(let $expr:pat =)* $cond:expr => $then:expr $(,)*) => { ... };
    ($(let $expr:pat =)* $cond:expr => $then:expr, else => $elsethen:expr $(,)*) => { ... };
    ($(let $expr:pat =)* $cond:expr => $then:expr, $($(let $expr2:pat =)* $else_cond:expr => $else_then:expr,)* else => $else_expr:expr $(,)*) => { ... };
    ($(let $expr:pat =)* $cond:expr => $then:expr, $($(let $expr2:pat =)* $more:expr => $more_then:expr $(,)* )*) => { ... };
    () => { ... };
}

A macro to make big else if conditions easier to read:

let s = "bateau";

if_match! {
    s == "voiture" => println!("It rolls!"),
    s == "avion"   => println!("It flies!"),
    s == "pieds"   => println!("It walks!"),
    s == "fusée"   => println!("It goes through space!"),
    s == "bateau"  => println!("It moves on water!"),
    else           => println!("I dont't know how it moves...")
}

You can use it just like you would use conditions:

let x = -1;

let result = if_match! {
    x >= 0 => "it's a positive number",
    else   => "it's a negative number",
};

assert_eq!(result, "it's a negative number");

And of course, the else condition is completely optional:

let x = 12;

if_match! {
    x & 1 == 0 => println!("it is even"),
    x & 1 == 1 => println!("it is odd"),
}

Want to use if let conditions too? Here you go:

let v = 12;
let y = if_match! {
    let 0 = 1 => 0,
    v < 1 => 1,
    v > 10 => 10,
    let 0 = 1 => 0,
    else => v
};
assert_eq!(y, 10);