Macro entity_component::join

macro_rules! join {
    (&$st:ident) => { ... };
    (&mut $st:ident) => { ... };
    ($($complex:tt)*) => { ... };
}

The join macro makes it very easy to iterate over multiple components of the same Entity at once.

There are two ways to use this macro: With a single component and with multiple.

When joining over a single component, simply provide the name of the Components<T> instance as an immutable or mutable reference. An iterator over the components will be returned. The iterator will be of type &T or &mut T elements.

Joining over multiple components offers a complete syntax to decide which components should or should not be matched. Here is an example:

let iter = join!(&storage1 && &mut storage2 || &mut storage3 && !&storage4);

Here, we first provide a bitset. This is due to a limitation with rust macros where creating variables inside of the macro and returning them is not allowed.

Then, we tell join to join over all entities that have:

• A component in storage1
• A component in either storage2 or storage3
• No component in storage4

We also specify that storage2 and storage3 should be accessed mutably.

Finally, we can iterate:

iter.for_each(|(component1, mut component2, mut component3, _)| {});

This iterator will be of type (Option<&T1>, Option<&mut T2>, ...).