Macro hydroflow::var_args

macro_rules! var_args {
    () => { ... };
    (...$a:pat $(,)? ) => { ... };
    (...$a:ty, $( $b:tt )+) => { ... };
    ($a:pat $(,)? ) => { ... };
    ($a:pat, $( $b:tt )+) => { ... };
}

Variadic patterns macro.

Used to pattern-match or “unpack” variadic tuples. This is used for function arguments, as well as in match, if/while let ..., let ... else, and for expressions.

Although it may somtimes be possible to use var_expr! in place of this macro, doing so may cause confusing errors.

use variadics::{var_args, var_expr, var_type};

fn my_fn(var_args!(a, b, c): var_type!(usize, &str, bool)) {
    println!("{} {} {}", a, b, c);
}
my_fn(var_expr!(12, "hello", false));

use variadics::{var_args, var_expr};

let val = var_expr!(true, Some("foo"), 2);
if let var_args!(true, Some(item), 0..=3) = val {
    println!("{}", item);
} else {
    unreachable!();
}

match var_expr!(true, Some(100), 5) {
    var_args!(false, _, _) => unreachable!(),
    var_args!(true, None, _) => unreachable!(),
    var_args!(true, Some(0..=10), _) => unreachable!(),
    var_args!(true, Some(a), b) => println!("{} {}", a, b),
}

The “spread” (or “splat”) syntax ... can be used to unpack the tail of a variadic. Note that unlike with the other macros, this macro (var_args!) only allows the spread syntax on the final argument.

let var_args!(a, b, ...list_c) = var_expr!("hi", 100, 0.5, false);
assert_eq!(var_expr!(0.5, false), list_c);