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use std::mem::transmute;
use std::sync::atomic::{AtomicU32, Ordering};
static NEXT: AtomicU32 = AtomicU32::new(1);
// Bit 0 and 1 for the kind
const KIND_BITS: u64 = 0x03;
#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq, PartialOrd, Ord)]
#[repr(u8)]
pub enum Kind
{
Entity = 2,
Component = 1,
}
/// Unique entity/component ID.
#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq, PartialOrd, Ord)]
pub struct Uid
{
inner: u64,
}
impl Uid
{
/// Returns a new unique entity/component ID.
pub fn new_unique(kind: Kind) -> Self
{
let id_part = NEXT.fetch_add(1, Ordering::Relaxed);
Self {
inner: (u64::from(id_part) << 32) | kind as u64,
}
}
#[must_use]
pub fn kind(&self) -> Kind
{
// SAFETY: The kind bits cannot be invalid since they are set using the Kind enum
// in the new_unique function
unsafe { transmute((self.inner & KIND_BITS) as u8) }
}
}
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