Const null

[bakcxoj]

It is not possible to do the following.

slotmap::new_key_type! {
    pub struct MyKey;
}

pub const fn null_key() -> MyKey {
    MyKey::null() // Error: cannot call non-const associated function
}

It's not even possible to fake it.

pub const fn null_key() -> MyKey {
    let key_data = KeyData::from_ffi(i32::MAX as u64);
    MyKey::from(key_data) // Error: cannot call non-const associated function
}