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Maps
Declaration

Define an empty map

ruby
map = []
java
Map map = new HashMap();
perl
%map = {}
groovy
def map = [:]
Map map = new HashMap();
scala
val map = mutable.Map.empty
val map = mutable.HashMap.empty[String, Int]
python
map = {}
cpp
Hashtable^ hash = gcnew Hashtable;
Generic::Dictionary<String^, String^>^ dict = gcnew Generic::Dictionary<String^, String^>();
std::map<int, std::string> m;
fsharp
let map = Map.empty
let map = new Generic.Dictionary<string, string>()
let map = new Hashtable()
erlang
Map = dict:new(),
Map = orddict:new(),
Map = gb_trees:empty(),
Map = ets:new(the_map_name, [set, private, {keypos, 1}]),
php
$map = array();
$map = array("" => "");

Define an unmodifiable empty map

ruby
map = [].freeze
java
Map empty = Collections.EMPTY_MAP;
SortedMap empty = MapUtils.EMPTY_SORTED_MAP;
perl
# perl does not provide unmodifiable maps/hashes, but you could use "constant
# functions", if you really need them

sub MAP () { {} }
groovy
empty = Collections.EMPTY_MAP
map = [:].asImmutable()
def empty = MapUtils.EMPTY_SORTED_MAP
def empty = ImmutableMap.of()
scala
val map = immutable.Map.empty
val map = immutable.TreeMap.empty[String, Int]
python
import collections
EmptyDict = collections.namedtuple("EmptyDict", "")
e = EmptyDict()
fsharp
// Most native fsharp data structures are immutable - updating a 'map' sees a modified copy created
let map = Map.empty
erlang

% Erlang data structures are immutable - updating a 'map' sees a modified copy created
Map = dict:new(),
php
/* It's not possible to define an array as a constant
* Instead we can use the serialize-function */

$fruits = array("apple", "banana", "orange");
define("FRUITS", serialize($fruits));
echo FRUITS; // a:3:{i:0;s:5:"apple";i:1;s:6:"banana";i:2;s:6:"orange";}
$my_fruits = unserialize(FRUITS); // and normal array again

Define an initial map

Define the map {circle:1, triangle:3, square:4}
ruby
shapes = {'circle'=>1, 'triangle'=>3, 'square'=>4}
shapes = Hash['circle', 1, 'triangle', 3, 'square', 4]
java
Map shapes = new HashMap();
shapes.put("circle", 1);
shapes.put("triangle", 3);
shapes.put("square", 4);
Map shapes = new HashMap() {{ put("circle",1); put("triangle",3); put("square",4); }}
perl
%map = (circle => 1, triangle => 3, square => 4);
groovy
shapes = [circle:1, triangle:3, square:4]
// if you require a specific type of map ...
LinkedHashMap shapes1 = [circle:1, triangle:3, square:4]
Properties shapes2 = [circle:1, triangle:3, square:4]
TreeMap shapes3 = [circle:1, triangle:3, square:4]
shapes4 = [circle:1, triangle:3, square:4] as ConcurrentHashMap // as variation
scala
val shapes = immutable.TreeMap("circle" -> 1, "triangle" -> 3, "square" -> 4)
val shapes = mutable.Map.empty[String, Int]

shapes += "circle" -> 1
shapes += "triangle" -> 3
shapes += "square" -> 4
var shapes = immutable.Map.empty[String, Int]

shapes = shapes + ("circle" -> 1)
shapes = shapes + ("triangle" -> 3)
shapes = shapes + ("square" -> 4)
python
shapes = {'circle': 1, 'square': 4, 'triangle': 2}
cpp
Hashtable^ shapes = gcnew Hashtable;

shapes->Add("circle", 1);
shapes->Add("triangle", 3);
shapes->Add("square", 4);
Generic::Dictionary<String^, int>^ shapes = gcnew Generic::Dictionary<String^, int>();

shapes->Add("circle", 1);
shapes->Add("triangle", 3);
shapes->Add("square", 4);
fsharp
let shapes = Map.of_list [("circle", 1); ("triangle", 3); ("square", 4)]
let shapes = Map.empty.Add("circle", 1).Add("triangle", 3).Add("square", 4)
let shapes = new Generic.Dictionary<string, int>()
shapes.Add("circle", 1)
shapes.Add("triangle", 3)
shapes.Add("square", 4)
erlang
Map = dict:from_list([{circle, 1}, {triangle, 3}, {square, 4}]),
Map0 = dict:new(),

% Erlang variables are 'single-assignment' i.e. they cannot be reassigned
Map1 = dict:store(circle, 1, Map0),
Map2 = dict:store(triangle, 3, Map1),
Map3 = dict:store(square, 4, Map2),
Map0 = gb_trees:empty(),

Map1 = gb_trees:enter(circle, 1, Map0),
Map2 = gb_trees:enter(triangle, 3, Map1),
Map3 = gb_trees:enter(square, 4, Map2),
Map = gb_trees:from_orddict(lists:keysort(1, [{circle, 1}, {triangle, 3}, {square, 4}])),
Map = ets:new(the_map_name, [ordered_set, private, {keypos, 1}]),
ets:insert(Map, [{circle, 1}, {triangle, 3}, {square, 4}]),
php
$map = array("circle" => 1, "triangle" => 3, "square" => 4);