Generators in dart with examples

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Dart generators :

Dart generators are used to produce a sequence of values lazily. We have two different types of generators called synchronous and asynchronous generators. In this post, I will show you how these generators works with examples.

 

Synchronous generator :

sync* is used to create one synchronous generator function. This is used just before the function body. Synchronous generators returns one Iterable object. For returning a object, yield is used.

For example :

Iterable<int> oddNumbersGenerator(n) sync* {
  while (n > 0) {
    if (n % 2 != 0) {
      print("yielding...");
      yield n;
    }
    n--;
  }
}
main(List<string> args) {
  oddNumbersGenerator(5).forEach(print);
}

oddNumbersGenerator is a synchronous generator. It returns one Iterable. It takes one number and for all numbers starting from it to 1, it delivers if it is odd. yield is used to deliver a value.

I have added one print statement before yield is called to help you understand how it works. It will print the below output :

yielding...
5
yielding...
3
yielding...
1

i.e. each time forEach is called, it generates the next value.

Dart synchronous generator

Asynchronous generator :

asynchronous generators are similar to synchronous generators. The only difference is that we need to use async* before the function body and it needs to return one Stream. It also uses yield to generate the next value.

We can change the above synchronous generator to asynchronous like below :

Stream<int> oddNumbersGenerator(n) async* {
  while (n > 0) {
    if (n % 2 != 0) {
      print("yielding...");
      yield n;
    }
    n--;
  }
}
main(List<string> args) {
  oddNumbersGenerator(5).forEach(print);
}

It will print the same output as the synchronous generator.

Dart asynchronous generator

Recursive generator :

We can call one generator function recursively. yield* function is used to call a function recursively. For example, we can change the above example to a recursive generator :

Iterable<int> oddNumbersGenerator(n) sync* {
  if (n > 0) {
    if (n % 2 != 0) {
      yield n;
    }
    yield* oddNumbersGenerator(n - 1);
  }
}
main(List<string> args) {
  oddNumbersGenerator(5).forEach(print);
}

If the value of n is greater than zero, it calls the same function recursively. If the value is not divisible by 2, it returns it.

Dart synchronous generator recursive

Similar tutorials :

Categories: dart

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