You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: rule_group_agg.rs
    path of file: ./repos/icu4x/components/experimental/src/transliterate/compile
    
    the code of the file until where you have to start completion: // This file is part of ICU4X. For terms of use, please see the file
// called LICENSE 
    
    fn push_rule_group(&mut self, group: ForwardRuleGroup<'p>) {
        match group {
            ForwardRuleGroup::Transform(transform_group) => {
                // because ForwardRuleGroup returns a different kind of group every time,
                // the previous group must have been a conversion group which pushed the
                // finished group pair into self.groups.
                debug_assert!(self.preceding_transform_group.is_none());
                self.preceding_transform_group = Some(transform_group);
            }
            ForwardRuleGroup::Conversion(conversion_group) => {
                let associated_transform_group = match self.preceding_transform_group.take() {
                    Some(transform_group) => transform_group,
                    // match arm is necessary if the first source-order rule group is a conversion group
                    None => Vec::new(),
                };
                self.groups
                    .push((associated_transform_group, conversion_group));
            }
        }
    }