transformation between Map to Set-CodePudding

in the following code I'm trying to transform between map to set so I used list as a middle since set doesn't allow keys and values I know there is easier ways to transform between these 2 but I want to know why it gave me "false" when I ran the script

void main() {
  List a = [];
  Map info = {"name": "mark", "age": "20"};
  info.forEach((key, value) {
    a.add(value);
  });

  a.toSet;
  print(a is Set);
}

CodePudding user response：

You've declared variable type of a as List, Therefor it will only can have list.

To convert set, use .toSet().

Now let say we still want to assign set inside a variable. In this case we can use dynamic data type.

void main() {
  dynamic a = [];
  Map info = {"name": "mark", "age": "20"};
  info.forEach((key, value) {
    a.add(value);
  });

  a = a.toSet();
  print(a is Set);
}

You can find more about dart type-system.

CodePudding user response：

Your code is printing false because the type of your variable a is still a List object.

If you check the documentation of the method toSet you will see that its prototype is the following:

Set<E> toSet()

The method toSet is not changing the type of your variable from List to Set, its returning a new value which you will have to keep inside another variable.

As mentioned by Yeasin you are declaring your variable a as List, to convert it to a Set object you can either type a as Set when declaring it:

Set a = {};

or, as you've tried, call the method toSet() but you will need to keep the return value in a new variable:

final mySet = a.toSet();

Note that instead of using a forEach you could directly convert as a Set your map by using the getter values:

Map info = {"name": "mark", "age": "20"};
final a = info.values.toSet();
print(a is Set);