Macro b_tree_map

macro_rules! b_tree_map {
    () => { ... };
    ($($key:expr => $val:expr),*) => { ... };
}

A macro to create a new BTreeMap, providing two usage options:

1. b_tree_map!() - Creates an empty BTreeMap.
2. b_tree_map!(key1 => value1, key2 => value2, ...) - Creates a BTreeMap containing the specified key-value pairs.