Optional.dart

Optional.dart is an implementation of the Optional type, inspired by Java 8's Optional class.

Optional helps avoid null reference errors by wrapping values in an object that holds information regarding whether the value is present or not.

For example, when applying a set of operations to a value, any of which might return null, you can get rid of the null checks by using Optional.map():

String getString() {
  // ..
  if (condition) {
    return null;
  } else {
    return "12";
  }
}

int calculateSomething(String str) {
  // ...
  if (someCondition) {
    return null;
  } else {
    return 3 + int.parse(str);
  }
} 

double calculateSomethingElse(int val) {
  // ...
  if (anotherCondition) {
    return null;
  } else {
    return val * 1.42;
  }
}

void main() {
  
  // before
  
  String str;
  int i;
  double d;
  
  str = getString();
  
  if (str != null) {
    i = calculateSomething(str);
  }
  
  if (i != null) {
    d = calculateSomethingElse(i);
  }
  
  if (d != null) {
    print(d);
  }
  
  // with Optional
  
  Optional.ofNullable(getString())
    .map(calculateSomething)
    .map(calculateSomethingElse)
    .ifPresent(print);
}

Libraries

optional
An implementation of the Optional type.
optional_internal