Macro instance_select

macro_rules! instance_select {
    ($Select:ident: $Base:path: $Class:ty { $( $Enum:ident($Param:ident = $Instance:ty) ),+ $(,)? }) => { ... };
}

The basic macro for making a union of entities.

This macro is the most generic version. You can find more specific versions in shape, material and object modules.

You can read more about the technique here.