Dart/Flutter Style Guide

We follow Effective Dart's style guide and documentation style guide.

Characters Line Limit.

An exception to Effective Dart is the characters line limit. Instead of 80 characters, we adhere to a 120 characters line limit.

Avoid null Assertions

Developers may be frustrated with converting nullable types to non-nullable types and forcefully convert a nullable type using the null assertion operator. However, doing so comes with a loss of static safety. This is undesirable in most cases since it circumvents the type system and is a potential source of bugs. Instead, the null-aware operator and checking if a value is null should be performed.

The following section contains counterexamples and the recommended alternatives.

Calling a method of a nullable object

// Bad
String foo = NullableObject!.bar();

// Good
String? foo = NullableObject?.bar();

String foo = NullableObject?.bar() ?? 'default value';

Assigning a nullable object to a non-nullable object

// Bad
String foo = bar!;

// Good
final foo = bar;
if (foo == null) {
  // Handle logic here
}

// foo is now non-nullable here

One caveat is tests. In tests, it is acceptable to use the null assertion operator. This is because the brevity and readability of tests outweighs the loss of static safety. Furthermore, tests are localized and are therefore easier to reason about.

See Dart null safety for more information.