macro_rules! ensure_columns_len { ($columns:ident) => { ... }; ($column_a:ident, $column_b:ident, $($column_n:ident),*) => { ... }; }
macro_rules! ensure_columns_len { ($columns:ident) => { ... }; ($column_a:ident, $column_b:ident, $($column_n:ident),*) => { ... }; }