Macro dep_obj::dep_system

macro_rules! dep_system {
    (
        $vis:vis fn $name:ident (self as $this:ident, $arena:ident : $Arena:ty) -> $System:ty {
            if mut { $field_mut:expr } else { $field:expr }
        }
    ) => { ... };
    (
        $vis:vis dyn fn $name:ident (self as $this:ident, $arena:ident : $Arena:ty) -> $System:tt {
            if mut { $field_mut:expr } else { $field:expr }
        }
    ) => { ... };
}