vec_new.rs

#![feature(macro_rules)]

macro_rules! vec_new(
    ($($e:expr),*) => ({
        // leading _ to allow empty construction without a warning.
        let mut _temp = ::std::vec::Vec::with_capacity(arity!($($e),*));
        $(_temp.push($e);)*
        _temp
    });
    ($($e:expr),+,) => (vec_new!($($e),+))
)

// Trust me, you *really* want the helper macros...
// If you attempt this without them, may God have mercy on your soul.
macro_rules! arity(
    ($($thing:expr),+) => (arity_expr!($($thing),*));
    ($($thing:pat),+) => (arity_pat!($($thing),*));
    () => (0);
)

macro_rules! arity_expr(
    ($head:expr, $($tail:expr),*) => (1 + arity_expr!($($tail),*));
    ($last:expr) => (1);
)

macro_rules! arity_pat(
    ($head:pat, $($tail:pat),*) => (1 + arity_pat!($($tail),*));
    ($last:pat) => (1);
)

fn test_arity() {
    assert!(arity!() == 0);

    // expr
    assert!(arity!(9) == 1);
    assert!(arity!(9,9,9) == 3);

    // ident - matched by expr
    assert!(arity!(Nine) == 1);
    assert!(arity!(Nine,Nine,Nine) == 3);

    // ty - matched by expr
    assert!(arity!(Option::<int>) == 1);
    assert!(arity!(Option::<int>,Option::<int>,Option::<int>) == 3);

    // block - matched by expr
    assert!(arity!({9;9}) == 1);
    assert!(arity!({9;9},{9;9},{9;9}) == 3);

    // pat
    assert!(arity!(foo @ _) == 1);
    assert!(arity!(foo @ _,foo @ _,foo @ _) == 3);

    println!("All tests pass");
}

fn main() {
    test_arity();
    let v = vec_new![7,8,9];
    println!("{}", v);
}