sparsey 0.13.3

Entity Component System based on sparse sets
Documentation 
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//! Entity storage and allocation.

mod entity_allocator;
mod entity_sparse_set;
mod entity_storage;
mod sparse_vec;

pub use self::sparse_vec::*;

pub(crate) use self::entity_allocator::*;
pub(crate) use self::entity_sparse_set::*;
pub(crate) use self::entity_storage::*;

use core::cmp::Ordering;
use core::fmt;
use core::num::NonZeroU32;

/// Uniquely identifies a set of components in a
/// [`World`](crate::world::World).
#[cfg_attr(target_pointer_width = "64", repr(align(8)))]
#[derive(Clone, Copy, PartialEq, Eq, Hash)]
pub struct Entity {
    /// The sparse index of the entity.
    pub index: u32,

    /// The version of the entity.
    pub version: Version,
}

impl Entity {
    /// Creates a new entity with the given `index` and `version`.
    #[inline]
    #[must_use]
    pub const fn new(index: u32, version: Version) -> Self {
        Self { index, version }
    }

    /// Creates a new entity with the given `index` and default
    /// version.
    #[inline]
    #[must_use]
    pub const fn with_index(index: u32) -> Self {
        Self {
            index,
            version: Version::FIRST,
        }
    }

    /// Returns the index of the entity extended to a [`usize`].
    #[inline]
    #[must_use]
    pub const fn sparse(&self) -> usize {
        self.index as usize
    }
}

impl PartialOrd for Entity {
    #[inline]
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl Ord for Entity {
    #[inline]
    fn cmp(&self, other: &Self) -> Ordering {
        self.version
            .cmp(&other.version)
            .then(self.index.cmp(&other.index))
    }
}

impl fmt::Debug for Entity {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct(stringify!(Entity))
            .field("index", &self.index)
            .field("version", &self.version.0)
            .finish()
    }
}

/// Version used to distinguish between entities with the same index.
#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
pub struct Version(pub NonZeroU32);

impl Version {
    /// The first valid version.
    pub const FIRST: Self = Self(NonZeroU32::MIN);

    /// The last valid version.
    pub const LAST: Self = Self(NonZeroU32::MAX);

    /// Returns the next available version, if any.
    #[inline]
    #[must_use]
    pub const fn next(&self) -> Option<Self> {
        match self.0.checked_add(1) {
            Some(version) => Some(Self(version)),
            None => None,
        }
    }
}

impl Default for Version {
    #[inline]
    fn default() -> Self {
        Self::FIRST
    }
}