Clone a List, Map or Set in Dart

by

Use of clone() in Java is tricky and questionable1,2. Effectively, clone() is a copy constructor and for that, the Dart List, Map and Set types each have a named constructor named .from() that perform a shallow copy; e.g. given these declarations

  Map<String, int> numMoons, moreMoons;
  numMoons = const <String,int>{ 'Mars' : 2, 'Jupiter' : 27 };
  List<String> planets, morePlanets;

you can use .from() like this:

  moreMoons = new Map<String,int>.from(numMoons)
    ..addAll({'Saturn' : 53 });
  planets = new List<String>.from(numMoons.keys);
  morePlanets = new List<String>.from(planets)
    ..add('Pluto');

Note that List.from() more generally accepts an iterator rather than just a List.

For sake of completeness, I should mention that the dart:html Node class defines a clone() method.

1 J. Bloch, “Effective Java” 2nd Ed., Item 11.
2 B. Venners, “Josh Bloch on Design: Copy Constructor versus Cloning“, 2002. Referenced from here3. Quote from the article:

If you’ve read the item about cloning in my book, especially if you read between the lines, you will know that I think clone is deeply broken. —J.Bloch

3 Dart Issue #6459, clone instance(object).

More Related Contents:

  1. what is difference between mutable and immutable property of collection in kotlin
  2. How to clone ArrayList and also clone its contents?
  3. Size-limited queue that holds last N elements in Java
  4. count vs length vs size in a collection
  5. MongoDB query multiple collections at once
  6. What is the best way to clone/deep copy a .NET generic Dictionary?
  7. How can I clone an Object (deep copy) in Dart?
  8. How can I have a collection of objects that differ by their associated type?
  9. IList vs IEnumerable for Collections on Entities
  10. Counter in Collections module Python
  11. Publishing/subscribing multiple subsets of the same server collection
  12. How to convert/transform a collection to another collection by element’s property?
  13. How do I remove repeated elements from ArrayList?
  14. Sorting an ArrayList of objects using a custom sorting order
  15. The argument type ‘String’ can’t be assigned to the parameter type ‘Uri’
  16. Deriving a trait results in unexpected compiler error, but the manual implementation works
  17. How to convert a Map to List in Java?
  18. Most efficient way to increment a Map value in Java
  19. Flutter – Wrap text on overflow, like insert ellipsis or fade
  20. Converting timestamp
  21. Lambda expression to convert array/List of String to array/List of Integers
  22. Combine multiple Collections into a single logical Collection?
  23. Java Ordered Map
  24. Deep copy vs Shallow Copy [duplicate]
  25. ASP JSON: Object not a collection
  26. Why doesn’t java.util.Set have get(int index)?
  27. Print array without brackets and commas
  28. Does Dart support enumerations?
  29. Collection initialization syntax in Visual Basic 2008?
  30. Why is my Entity Framework Code First proxy collection null and why can’t I set it?

Leave a Comment