Sometimes we run into a case when a function logically needs to return multiple values. Some examples are returning coordinates of a point, returning some statistical data, returning error information like the error code and the message, etc.
Important
Records require a language version of at least 3.0.
Previously, when we wanted to return more than one object from a function, we had to create an additional class or add a package like Tuple.
The following code snippet shows that to return the name and age from a function, we had to create a class called User:
void main() {
final user = getUser();
print('Name: ${user.name}'); // Prints 'John'
print('Age: ${user.age}'); // Prints '30'
}
User getUser() {
return User('John', 30);
}
class User {
final String name;
final int age;
User(this.name, this.age);
}Now let’s see the difference using records.
void main() {
final user = getUser();
print('Name: ${user.name}'); // Prints 'John'
print('Age: ${user.age}'); // Prints '30'
}
({String name, int age}) getUser() {
return (name: 'John', age: 30);
}We can see that using records, it is not necessary to create a User class.
Records Syntax
Records expressions are comma-delimited lists of named or positional fields, enclosed in parentheses:
void main() {
final user = (name: 'John', age: 30);
print('Name: ${user.name}'); // Prints 'John'
print('Age: ${user.age}'); // Prints '30'
final anime = ('One Piece', 500);
print('Name: ${anime.$1}'); // Prints 'One Piece'
print('Episodes: ${anime.$2}'); // Prints '500'
final record = ('first', a: 2, b: true, 'last');
print(record.$1); // Prints 'first'
print(record.a); // Prints 2
print(record.b); // Prints true
print(record.$2); // Prints 'last'
}Records and Pattern Destructuring
We can even use destructuring, which is a pattern matching technique, to extract and assign values from a data structure into individual variables concisely and efficiently. The code would look like this:
void main() {
final (:name, :age) = getUser();
print('Name: $name'); // Prints 'John'
print('Age: $age'); // Prints '30'
}
({String name, int age}) getUser() {
return (name: 'John', age: 30);
}References