Getting ready

Before we dive into the code, let's diverge briefly to the builder pattern. Builders are a type of class whose only purpose is to build other classes. They are often used for complex objects with many properties. It can get to a point where standard constructors become impractical and unwieldy because they are too large. This is the problem the builder pattern solves. It is a special kind of class whose only job is to configure and create other classes.

This is how we would accomplish the builder pattern without the cascade operator:

class UrlBuilder {
  String _scheme;
  String _host;
  String _path;

  UrlBuilder setScheme(String value) {
    _scheme = value;
    return this;
  }

  UrlBuilder setHost(String value) {
    _host = value;
    return this;
  }

  UrlBuilder setPath(String value) {
    _path = value;
    return this;
  }

  String build() {
    assert(_scheme != null);
    assert(_host != null);
    assert(_path != null);

    return '$_scheme://$_host/$_path';
  }
}

void main() {
  final url = UrlBuilder()
      .setScheme('https')
      .setHost('dart.dev')
      .setPath('/guides/language/language-tour#cascade-notation-')
      .build();
  
  print(url);
}

This is very verbose. Dart can implement this pattern without any setup.

Create a new file in your project or type the code of this recipe in Dartpad.