pub fn merge_type(&self) -> Type {
        use self::BuilderKind::*;
        use self::Type::*;
        match *self {
            Appender(ref elem) => *elem.clone(),
            Merger(ref elem, _) => *elem.clone(),
            DictMerger(ref key, ref value, _) => Struct(vec![*key.clone(), *value.clone()]),
            GroupMerger(ref key, ref value) => Struct(vec![*key.clone(), *value.clone()]),
            VecMerger(ref elem, _) => Struct(vec![Scalar(I64), *elem.clone()]),
        }
    }
Returns the type merged into this `BuilderKind`.
weld/src/ast/ast.rs