Dart supports many different types of collections, or data types that contain multiple values. The most common collections:

• List (known as an array in some languages)
• Set
• Map

Maps

A map, also known commonly as a dictionary or hash, is an unordered collection of key-value pairs. Maps pair a key with a value for easy, fast retrieval. Like lists and sets, maps can be declared with a constructor or literal syntax.

// literal syntax
var dogsIvePet = {
  'Golden Retriever': ['Cowboy', 'Jack'],
  'Laberdoodles': ['Wallace', 'Phoebe'], 
  'Shepards': ['Doug', 'Steak'],
}
// constructor syntax
var dogsIWantToPet = Map();
// create a key called 'Border Collie' and assign it's value
dogsIWantToPet['Border Collie'] = ['Mike', 'Jackson'];

Like other collections, there are many class members on the Map class that make it more convenient to manipulate. A couple of them are:

• remove(key)
• keys
• values
• length
• isEmpty and isNotEmpty
• containsKey(key)

var dogsIvePet = {
  'Golden Retriever': ['Cowboy', 'Jack'],
  'Laberdoodles': ['Wallace', 'Phoebe'], 
  'Shepherds': ['Doug', 'Steak'],
}
// remove an item
dogsIvePet.remove('Laberdoodles');
// length gives the number of key-value pairs
print(dogsIvePet.length);
// output: 2
print(dogsIvePet.keys);
// output: ['Golden Retriever', 'Shepherds']