#![cfg_attr(feature = "const-fn", feature(const_fn))]

#[cfg(feature = "foo")]
fn foo() {
    println!("its foo");
}

#[cfg(not(feature = "foo"))]
fn foo() {
    println!("its not foo");
}

macro_rules! const_fn {
    ($($f:tt)*) => (
        #[cfg(feature = "const-fn")]
        const $($f)*

        #[cfg(not(feature = "const-fn"))]
        $($f)*
    );
}

struct A;


impl A {
    const_fn!(fn new() -> A { A });
}

fn main() {
    foo();
    let a = A::new();
}