CODEWITHSUNDEEP
dart
Arthur Bertemes
Arthur Bertemes

Reputation: 1286

Do Enums in Dart have comparison operators?

I come from a Kotlin background and I used to the fact that enums there implements Comparable, which allows me do something like below:

Given a enum

enum class Fruit{
  APPLE,
  BANANA,
  ORANGE,
}

I could use the operators <, >, <= or >=, to compare any occurrence of this enum, like:

APPLE < BANANA -> true
ORANGE < BANANA -> false

I wonder if dart has the same by default or if I have to define custom operators to any enum I might need that.

Upvotes: 8

Views: 7770

Answers (4)

Erik
Erik

Reputation: 21

If you want to define your own order, then this is a simple and compact solution:

enum Fruit {
  APPLE, // index 0
  BANANA, // index 1
  ORANGE; // index 2

  bool operator >(Similarity other) => index > other.index; 
  bool operator <(Similarity other) => index < other.index;
  bool operator >=(Similarity other) => index >= other.index;
  bool operator <=(Similarity other) => index <= other.index;
}

Note that the order is reversed. ORANGE > BANANA = true

If you want to compare the words APPLE, BANANA and ORANGE instead, then you can use this:

enum Fruit {
  APPLE,
  BANANA,
  ORANGE;

  bool operator >(Similarity other) => toString().compareTo(other.toString()) > 0;
  bool operator <(Similarity other) => toString().compareTo(other.toString()) < 0;
  bool operator >=(Similarity other) => toString().compareTo(other.toString()) >= 0;
  bool operator <=(Similarity other) => toString().compareTo(other.toString()) <= 0;
}

Upvotes: 2

jamesdlin
jamesdlin

Reputation: 90155

It's easy to check Enum documentation or try it yourself to see that Enum classes do not provide operator <, operator >, etc.

Dart 2.15 does add an Enum.compareByIndex method, and you also can add extension methods to Enums:

extension EnumComparisonOperators<T extends Enum> on T {
  bool operator <(T other) {
    return index < other.index;
  }

  bool operator <=(T other) {
    return index <= other.index;
  }

  bool operator >(T other) {
    return index > other.index;
  }

  bool operator >=(T other) {
    return index >= other.index;
  }
}

Upvotes: 7

Michael Bushe
Michael Bushe

Reputation: 1571

Since 2.15, statically:

compareByIndex<T extends Enum>(T value1, T value2) → int
    Compares two enum values by their index. [...]
    @Since("2.15")
compareByName<T extends Enum>(T value1, T value2) → int
    Compares enum values by name. [...]
    @Since("2.15")

https://api.dart.dev/stable/2.16.1/dart-core/Enum-class.html

Upvotes: 1

TwoGirls
TwoGirls

Reputation: 49

As explained in other comments, you can also create your own operator and use it.

Try the code below to see how to handle it without creating an operator.

enum Fruit{
  APPLE,
  BANANA,
  ORANGE,
}

void main() {

  print(Fruit.APPLE.index == 0);
  print(Fruit.BANANA.index == 1);
  print(Fruit.ORANGE.index == 2);
  
  if( Fruit.APPLE.index < Fruit.BANANA.index ){
    // Write your code here
    print("Example");
  }
  
}

result

true
true
true
Example

Upvotes: 2

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