CODEWITHSUNDEEP
dartsyntax
Ravi Arora
Ravi Arora

Reputation: 121

Need help understanding => symbol in Dart

I came across the following Dart code while reading about first where. I wanted to understand what exactly is happening in this code as this is some syntax I am not familiar with, particularly the "=>" symbols.

void main() {
  final list = List<Book>.generate(10, (id) => Book(id));
  Book findBook(int id) => list.firstWhere((book) => book.id == id);

  print(findBook(2).name);
  print(findBook(4).name);
  print(findBook(6).name);
}

class Book {
  final int id;

  String get name => "Book$id";

  Book(this.id);
}

Upvotes: 0

Views: 65

Answers (1)

Lulupointu
Lulupointu

Reputation: 3594

This is what is called Syntaxic sugar. It does not provide a special functionality but makes it easier for developer to write and read code.

In the cas of the => symbol, it is a shortcut for a function containing only a return statement. So those two definitions are exactly the same:

String main() {
    return "Hello World"
}

String main() => "Hello World";

Note however, how the second one is way more readable.

So in your case if we unwrap everything your code would become:

void main() {
  final list = List<Book>.generate(10, (id) {
    return Book(id);
  });
  Book findBook(int id) {
    return list.firstWhere((book) {
      return book.id == id;
    });
  }

  print(findBook(2).name);
  print(findBook(4).name);
  print(findBook(6).name);
}

class Book {
  final int id;

  String get name {
    return "Book$id";
  }

  Book(this.id);
}

Upvotes: 3

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