ty_map_gen

A type projecting map generator.

Syntax

type_map!(
    /// Asset Map
    #[derive(Clone, PartialEq, Eq)]
    pub AssetMap where T [Asset] => Handle<T> [Clone + Eq] as HashMap
);

This creates a type that projects T (a generic) to Handle<T> (roughly):

pub struct AssetMap(HashMap<TypeId, Box<dyn Any>>)

with access methods (roughly):

fn get<T: Asset + 'static>(&self) -> Option<&Handle<T>> where Handle<T>: Clone + Eq {
    self.0.get(TypeId::of::<T>()).and_then(|v| v.downcast_ref())
}

Since all values stored in the map are Clone and Eq, they can be derived.

The as HashMap field accepts all structs that has the same api as HashMap, this includes BTreeMap and third party types like FxHashMap or VecMap. To specify a custom hasher, you must define a new type with signature Map<Key, Value>.

Bounds

Bounds (in braces []) are optional in the macro. The bounds on the right hand side must be object safe, excluding Clone, PartialEq, Eq, Ord, PartialOrd, Hash and Serialize, which are special handled. Additionally only one trait from std::cmp is allowed to be specified. If you need Send and Sync this is where to add them.

Currently the right hand side uses a unique scope, therefore you must supply fully qualified trait paths.

Methods and Implementations

By default these methods are generated by the macro:

Default, new, is_empty, len, get, get_mut, insert, remove, clear, extend.

Double Keys

type_map!(
    /// Asset Map
    #[derive(Clone, PartialEq, Eq)]
    pub AssetMap where (T, String) [Asset] => Handle<T> [Clone + Eq] as HashMap
);

This adds another key to the map, with access methods (roughly):

fn get<T: Asset + 'static>(&self, key: &Q) -> Option<&Handle<T>> where Handle<T>: Clone + Eq {
    self.0.get(&(TypeId::of::<T>(), key)).and_then(|v| v.downcast_ref())
}

Performance

This crate has faster lookup (get and get_mut) than a naive implementation with Box<dyn Any> since downcasting is unchecked.

License

License under either of

Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0) MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT) at your option.

Contribution

Contributions are welcome!

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.