Collection If in Dart

Introduction

Collection if is a Dart feature that lets you conditionally include elements in a collection literal using an if expression directly inside the collection. No temporary variables or multi-step logic needed.

Why It Matters

Building dynamic lists or maps where certain items should only be included based on a condition is a common task. Collection if keeps this logic inline and readable, eliminating the need to build the collection in multiple steps.

Syntax

var list = [
  element1,
  if (condition) element2,
  if (condition) element3 else element4,
];

Code Example

void main() {
  bool isAdmin = true;
  bool hasPremium = false;

  // Conditionally add menu items
  var menuItems = [
    'Home',
    'Profile',
    if (isAdmin) 'Admin Panel',
    if (hasPremium) 'Premium Content' else 'Upgrade to Premium',
  ];
  print(menuItems);

  // In a Map
  String? promoCode;
  var order = {
    'product': 'Dart Book',
    'price': 29.99,
    if (promoCode != null) 'promo': promoCode,
  };
  print(order);

  // With else
  bool isDarkMode = true;
  var themeColors = [
    if (isDarkMode) '#1a1a2e' else '#ffffff',
    if (isDarkMode) '#16213e' else '#f5f5f5',
  ];
  print(themeColors);

  // Nested conditions
  int age = 25;
  bool isStudent = false;
  var pricing = [
    'Standard: \$10',
    if (age < 18) 'Child Discount: \$5',
    if (isStudent) 'Student Discount: \$7',
    if (age >= 60) 'Senior Discount: \$6',
  ];
  print(pricing);
}

[Home, Profile, Admin Panel, Upgrade to Premium]
{product: Dart Book, price: 29.99}
[#1a1a2e, #16213e]
[Standard: $10]

Explanation

• if (condition) element includes element in the collection only when condition is true.
• if (condition) elementA else elementB includes elementA when true, otherwise elementB.
• Multiple if entries can appear in the same collection literal.
• Collection if works in List, Set, and Map literals.

Notes

• The condition inside collection if must be a boolean expression.
• You can only include one element per if — use the spread operator with a sub-list if you need multiple conditional elements.
• Collection if is evaluated at the time the collection literal is created.

Common Mistakes

• Trying to include multiple elements with a single if — use if (cond) ...[a, b] instead.
• Forgetting that the else branch is optional — if omitted and the condition is false, nothing is added.
• Using collection if when a where() filter or ?? would be more appropriate.

Summary

Collection if allows you to conditionally include elements directly inside collection literals. It supports if and if-else forms and works with List, Set, and Map. To conditionally include multiple elements, combine collection if with the spread operator. This feature makes dynamic collection construction clean and expressive.