Generators

Prerequisite: Iteration, Iterator , Iterable

void main(){
  
  
  List<int> myList = [1,2,4,5,7];
  
  
  for(int i in myList){
    
    print(i);
    
    
  }
  
}

void main(){
  
  
  // Example with Map 
  
   Map<int,String> myIterable  ={
     
     
     1:"Apple",
     2:"Orange",
     3:"Banana"
   };
  
  
  
  for(var i in myIterable.keys){
    
    
      print(i);
    
  }
  
  
  for(var i in myIterable.values){
    
    
      print(i);
    
  }
  
  
  
}

In simple words , iterable is something you can loop over or a collection of values that can be accessed sequentially

Iterator is something that remember can "where it is " i.e. current position during iteration

Documentation

Iterable collectionsdart_lang

Sync Generators

There are two types of Generators in Dart

Synchronous Generator Returns an iterable
Asynchronous Generator Returns a stream

In a normal function you would expect the function body to execute when you call the function , but in case of generator it doesn't execute

void main() {
  print("Start of main");

  Iterable<int> numbers = getNumbers(6);

  print("End of main ");
}

Iterable<int> getNumbers(int number) sync* {
  print("Number Generation Started");

  for (int i = 0; i < 0; i++) {
    yield i;
  }

  print("Number Generation ended");
}

The generator starts executing when you start iterating over iterable it returned

void main() {
  print("Start of main");

  Iterable<int> numbers = getNumbers(6);

  for (var i in numbers) {
    print(i);
  }

  print("End of main ");
}

Iterable<int> getNumbers(int number) sync* {
  print("Number Generation Started");

  for (int i = 0; i < number; i++) {
    yield i;
  }

  print("Number Generation ended");
}

You can think of Generators as a kind of special function . In normal function when you call it , it executes the statements inside it , then returns a value . In case of generators it returns an iterator . When you iterate over the values it runs the statements in the generator and every time it hits "yield" it produces a value ("yield" pauses the execution of the generator and returns a value) So you are able to call generators multiple times and every time it generates a value for you , hence the name . Until you exhaust the generator , you can keep calling it and it will generate a value

Async Generators

PreviousStreams NextMicrotask and Zones

Last updated 5 years ago

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