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use std::any::Any;

use crate::storage::UnprotectedStorage;

/// Abstract component type.
/// Doesn't have to be Copy or even Clone.
///
/// ## Storages
///
/// Components are stored in separated collections for maximum
/// cache efficiency. The `Storage` associated type allows
/// to specify which collection should be used.
/// Depending on how many entities have this component and how
/// often it is accessed, you will want different storages.
///
/// The most common ones are `VecStorage` (use if almost every entity has that
/// component), `DenseVecStorage` (if you expect many entities to have the
/// component) and `HashMapStorage` (for very rare components).
///
/// ## Examples
///
/// ```
/// use specs::prelude::*;
///
/// pub struct Position {
///     pub x: f32,
///     pub y: f32,
/// }
///
/// impl Component for Position {
///     type Storage = VecStorage<Self>;
/// }
/// ```
///
/// ```
/// use specs::prelude::*;
///
/// pub enum Light {
///     // (Variants would have additional data)
///     Directional,
///     SpotLight,
/// }
///
/// impl Component for Light {
///     type Storage = DenseVecStorage<Self>;
/// }
/// ```
///
/// ```
/// use specs::{prelude::*, storage::HashMapStorage};
///
/// pub struct Camera {
///     // In an ECS, the camera would not itself have a position;
///     // you would just attach a `Position` component to the same
///     // entity.
///     matrix: [f32; 16],
/// }
///
/// impl Component for Camera {
///     type Storage = HashMapStorage<Self>;
/// }
/// ```
pub trait Component: Any + Sized {
    /// Associated storage type for this component.
    #[cfg(feature = "parallel")]
    type Storage: UnprotectedStorage<Self> + Any + Send + Sync;

    /// Associated storage type for this component.
    #[cfg(not(feature = "parallel"))]
    type Storage: UnprotectedStorage<Self> + Any;
}