bevy/crates/bevy_utils/src/label.rs

//! Traits used by label implementations

use std::{
    any::Any,
    hash::{Hash, Hasher},
};

pub trait DynEq: Any {
    fn as_any(&self) -> &dyn Any;

    fn dyn_eq(&self, other: &dyn DynEq) -> bool;
}

impl<T> DynEq for T
where
    T: Any + Eq,
{
    fn as_any(&self) -> &dyn Any {
        self
    }

    fn dyn_eq(&self, other: &dyn DynEq) -> bool {
        if let Some(other) = other.as_any().downcast_ref::<T>() {
            return self == other;
        }
        false
    }
}

pub trait DynHash: DynEq {
    fn as_dyn_eq(&self) -> &dyn DynEq;

    fn dyn_hash(&self, state: &mut dyn Hasher);
}

impl<T> DynHash for T
where
    T: DynEq + Hash,
{
    fn as_dyn_eq(&self) -> &dyn DynEq {
        self
    }

    fn dyn_hash(&self, mut state: &mut dyn Hasher) {
        T::hash(self, &mut state);
        self.type_id().hash(&mut state);
    }
}

#[doc(hidden)]
pub use concat_idents::concat_idents;

/// Macro to define a new label trait
///
/// # Example
///
/// ```
/// # use bevy_utils::define_label;
/// define_label!(MyNewLabelTrait);
/// ```
#[macro_export]
macro_rules! define_label {
    ($label_name:ident) => {
        $crate::label::concat_idents!(id_name = $label_name, Id {

            /// Stores one of a set of strongly-typed labels for a class of objects.
            #[derive(Clone, Copy, PartialEq, Eq, Hash)]
            pub struct id_name(::core::any::TypeId, &'static str);

            impl ::core::fmt::Debug for id_name {
                fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
                    write!(f, "{}", self.1)
                }
            }

            /// Types that can be converted to a(n) [`id_name`].
            ///
            /// Check the docs for [`define_label`](bevy_ecs::define_label) for more info.
            pub trait $label_name: 'static {
                /// Converts this type into an opaque, strongly-typed label.
                fn as_label(&self) -> id_name {
                    let id = self.type_id();
                    let label = self.as_str();
                    id_name(id, label)
                }
                /// Returns the [`TypeId`] used to differentiate labels.
                fn type_id(&self) -> ::core::any::TypeId {
                    ::core::any::TypeId::of::<Self>()
                }
                /// Returns the representation of this label as a string literal.
                ///
                /// In cases where you absolutely need a label to be determined at runtime,
                /// you can use [`Box::leak`] to get a `'static` reference.
                fn as_str(&self) -> &'static str;
            }

            impl $label_name for id_name {
                fn as_label(&self) -> Self {
                    *self
                }
                fn type_id(&self) -> ::core::any::TypeId {
                    self.0
                }
                fn as_str(&self) -> &'static str {
                    self.1
                }
            }

            impl $label_name for &'static str {
                fn as_str(&self) -> Self {
                    self
                }
            }
        });
    };
}