Macro defaultbtreemap 

macro_rules! defaultbtreemap {
    (@single $($x:tt)*) => { ... };
    (@count $($rest:expr),*) => { ... };
    (@btreemap $($key:expr => $value:expr),*) => { ... };
    ($($key:expr => $value:expr,)+) => { ... };
    ($($key:expr => $value:expr),*) => { ... };
    ($default:expr$(, $key:expr => $value:expr)+ ,) => { ... };
    ($default:expr$(, $key:expr => $value:expr)*) => { ... };
}

The defaultbtreemap! macro can be used to easily initialize a DefaultBTreeMap in the following ways:

// An empty map with the default as default
let _: DefaultBTreeMap<i32, i32> = defaultbtreemap!{};

// An empty map with a specified default
let _: DefaultBTreeMap<i32, i32> = defaultbtreemap!{5};

// A prefilled map with the default as the default
let _: DefaultBTreeMap<i32, i32> = defaultbtreemap!{
    1 => 10,
    5 => 20,
    6 => 30,
};

// A prefilled map with a custom default
let _: DefaultBTreeMap<i32, i32> = defaultbtreemap!{
    5,
    1 => 10,
    5 => 20,
    6 => 30,
};