Spread Operator and Collection Literals in Dart

Spread Operator ...

The spread operator ... inserts all elements of a collection into another collection literal:

var first = [1, 2, 3];
var second = [4, 5, 6];

var combined = [...first, ...second];
print(combined);  // [1, 2, 3, 4, 5, 6]

// Works with sets and maps too
var setA = {1, 2, 3};
var setB = {3, 4, 5};
var merged = {...setA, ...setB};
print(merged);  // {1, 2, 3, 4, 5}

var defaults = {'theme': 'light', 'lang': 'en'};
var override = {'theme': 'dark'};
var config = {...defaults, ...override};
print(config);  // {theme: dark, lang: en}

Null-Aware Spread ...?

List<int>? extra = null;
var result = [1, 2, ...?extra, 3];
print(result);  // [1, 2, 3] — null spread adds nothing

Collection If

Include elements conditionally inside a collection literal:

bool isAdmin = true;
var menu = [
  'Home',
  'Profile',
  if (isAdmin) 'Admin Panel',
  'Logout',
];
print(menu);  // [Home, Profile, Admin Panel, Logout]

Collection For

Generate multiple elements inside a collection literal using a for loop:

var squares = [for (int i = 1; i <= 5; i++) i * i];
print(squares);  // [1, 4, 9, 16, 25]

var greetings = [for (var name in ['Alice', 'Bob']) 'Hello, $name!'];
print(greetings);  // [Hello, Alice!, Hello, Bob!]

Full Example

void main() {
  var baseItems = ['apple', 'banana'];
  var extraItems = ['cherry', 'date'];
  bool includePremium = true;

  var cart = [
    ...baseItems,
    ...?extraItems,
    if (includePremium) 'truffle',
    for (var i = 1; i <= 2; i++) 'gift_$i',
  ];

  print(cart);
  // [apple, banana, cherry, date, truffle, gift_1, gift_2]
}

[apple, banana, cherry, date, truffle, gift_1, gift_2]

🧠 Quiz

Summary

The spread operator ... merges collections inline. Use ...? for null-safe spreading. Collection if conditionally includes elements. Collection for generates multiple elements from a loop — all inside a single collection literal, without intermediate variables.