Function ast_node_as 

pub unsafe fn ast_node_as<T>(node: *mut AstNode) -> *mut T
where
    T: AstNodeClass,

node->as<T>() — downcast a base-node pointer to *mut T, or null when the dynamic type does not match.

Safety

node must be null or point to a live node whose first field is (transitively) an AstNode — i.e. any of the generated #[repr(C)] node structs. This is the same precondition as the C++ static_cast<T*>(this) it replaces.