Macro into_bmap 

macro_rules! into_bmap {
    (
    $( $key : expr => $value : expr ),* $( , )?
  ) => { ... };
}

Creates a BTreeMap from a list of key-value pairs.

The into_bmap macro facilitates the convenient creation of a BTreeMap with initial elements. Keys and values passed to the macro are automatically converted into the map’s key and value types using .into(), enabling the use of literals or values of different, but convertible types.

Note: The into_bmap macro relies on the .into() method to convert each key and value into the target types of the BTreeMap. This means that the keys and values must be compatible with the Into< K > and Into< V > traits for the key type K and value type V used in the BTreeMap. Also, this means that sometimes you must specify the type of collection’s items.

Origin

This collection is reexported from alloc.

Syntax

The macro can be called with a comma-separated list of key-value pairs. A trailing comma is optional.

// BTreeMap of &str to i32
let map1 : BTreeMap< &str, i32 > = into_bmap!( "one" => 1, "two" => 2, "three" => 3 );

// BTreeMap of String to String
let map2 : BTreeMap< String, String > = into_bmap!{ "name" => "value" };

// With trailing comma
let map3 : BTreeMap< i32, &str > = into_bmap!( 1 => "one", 2 => "two", 3 => "three", );

Parameters

• $( $key:expr => $value:expr ),* $( , )?: A comma-separated list of key-value pairs to insert into the BTreeMap. Each key and value can be of any type that implements the Into< K > and Into< V > traits, where K and V are the types stored in the BTreeMap as keys and values, respectively.

Returns

Returns a BTreeMap containing all the specified key-value pairs. The map’s capacity is automatically determined based on the number of elements provided.

Example

Basic usage with string slices and integer values:

let map : BTreeMap< &str, i32 > = into_bmap!( "one" => 1, "two" => 2, "three" => 3 );
assert_eq!( map.get( "one" ), Some( &1 ) );
assert_eq!( map.get( "two" ), Some( &2 ) );
assert_eq!( map.get( "three" ), Some( &3 ) );

Example

Using with different types that implement Into< K > and Into< V >:

let months : BTreeMap< String, i32 > = into_bmap!( "January" => 1, "February" => 2, "March" => 3 );
assert_eq!( months.get( &"January".to_string() ), Some( &1 ) );
assert_eq!( months.get( &"February".to_string() ), Some( &2 ) );

Example

Creating a BTreeMap of integers to strings from literals:

let numbers : BTreeMap< i32, String > = into_bmap!( 1 => "one", 2 => "two", 3 => "three" );
assert_eq!( numbers.get( &1 ), Some( &"one".to_string() ) );
assert_eq!( numbers.get( &2 ), Some( &"two".to_string() ) );
assert_eq!( numbers.get( &3 ), Some( &"three".to_string() ) );