// `unsafe` is a permission marker, not a semantic change: it does not alter
// what the enclosed operations mean, so the block is transparent and each
// operation inside still goes through the ordinary lowering.
//
// Nim's closures capture by reference, as Rust's non-`move` closures do.

fn apply(f: impl Fn(i32) -> i32, x: i32) -> i32 {
    f(x)
}

fn twice(x: i32) -> i32 {
    x * 2
}

fn halve(n: i32) -> Result<i32, i32> {
    if n % 2 == 0 { Ok(n / 2) } else { Err(n) }
}

fn as_str(b: &[u8]) -> &str {
    unsafe { core::str::from_utf8_unchecked(b) }
}

fn main() {
    let add_one = |x: i32| x + 1;
    println!("{}", apply(add_one, 10));
    println!("{}", apply(twice, 10));
    println!("{}", apply(|x: i32| x * x, 7));

    // A closure capturing an enclosing binding, by reference.
    let base: i32 = 100;
    let shift = |x: i32| x + base;
    println!("{}", apply(shift, 5));

    // `.map` over a Result: the closure's parameter type comes from the
    // receiver, and the error branch is carried through untouched.
    println!("{:?}", halve(8).map(|v| v * 10));
    println!("{:?}", halve(7).map(|v| v * 10));

    // `&str` is a view of someone else's bytes, not a copy.
    let bytes: Vec<u8> = vec![104, 105];
    println!("{} {}", as_str(&bytes), as_str(&bytes).len());

    let n: i32 = unsafe { twice(21) };
    println!("{}", n);
}