CODEWITHSUNDEEP
dart
Malwinder Singh
Malwinder Singh

Reputation: 7050

Chaining method calls

According to official Dart documentation, it is mentioned that:

Chaining method calls

a..b = true..c = 5;

Cascade used for chaining access to methods and other members. Equivalent:

a.b = true; a.c = 5;

Can someone explain the meaning of the above lines?

Upvotes: 2

Views: 819

Answers (2)

Malwinder Singh
Malwinder Singh

Reputation: 7050

Cascades

To perform a sequence of operations on the same object, use cascades (..). We’ve all seen an expression like this:

myObject.someMethod()

It invokes someMethod() on myObject, and the result of the expression is the return value of someMethod().

Here’s the same expression with a cascade:

myObject..someMethod()

Although it still invokes someMethod() on myObject, the result of the expression isn’t the return value — it’s a reference to myObject! Using cascades, you can chain together operations that would otherwise require separate statements. For example, consider this code:

var button = querySelector('#confirm');
button.text = 'Confirm';
button.classes.add('important');
button.onClick.listen((e) => window.alert('Confirmed!'));

With cascades, the code becomes much shorter, and you don’t need the button variable:

querySelector('#confirm')
..text = 'Confirm'
..classes.add('important')
..onClick.listen((e) => window.alert('Confirmed!'));

Upvotes: 1

Harshvardhan Joshi
Harshvardhan Joshi

Reputation: 3193

Consider user as an instace of following class:

class User {
  int age;
  String firstName;
  String lastName;
}

Now you can update data in user as following:

user.age = 5;
user.firstName = 'John';
user.lastName = 'Doe';

but if you use chaining access as described in the documentation. Then it will look something like this:

user..age = 5
    ..firstName = 'John'
    ..lastName = 'Doe';

Note: sequence of assignment of the properties does not matter, but it might be of importance while calling functions or methods like this.

Just a simple & random example:

painter..computeLayout()
    ..initializePaint()
    ..render();

above is same as:

painter.computeLayout();
painter.initializePaint();
painter.render();

in the above example all of the methods were called on painter object/instance but the sequence here must be followed as without paint or layout the render will not work.

Upvotes: 3

Related Questions