dart-modern-features

Dart Modern Features

1. When to use this skill

Use this skill when:

• Writing or reviewing Dart code targeting Dart 3.0 or later.
• Refactoring legacy Dart code to use modern, concise, and safe features.
• Looking for idiomatic ways to handle multiple return values, deep data extraction, or exhaustive checking.

Discovery

To find candidates for modernization:

Switch Expressions

Search for switch statements where every case assigns to the same variable or returns:

• Regex: switch\s*\([^)]+\)\s*\{\s*case

Pattern Matching Candidates

Search for manual map or JSON property extraction and type checking:

• Regex: containsKey\(['"][^'"]+['"]\)
• Regex: json\[['"][^'"]+['"]\]\s+is\s+

Null-Aware Elements

Search for collection if statements checking for null:

• Regex: if\s*\(\w+\s*!=\s*null\)\s*\w+

Digit Separators

Search for long numbers without separators:

• Regex: \b\d{6,}\b (Matches numbers with 6 or more digits).

2. Features

Records

Use records as anonymous, immutable, aggregate structures to bundle multiple objects without defining a custom class. Prefer them for returning multiple values from a function or grouping related data temporarily.

Avoid: Creating a dedicated class for simple multiple-value returns.

class UserResult {
  final String name;
  final int age;
  UserResult(this.name, this.age);
}

UserResult fetchUser() {
  return UserResult('Alice', 42);
}

Prefer: Using records to bundle types seamlessly on the fly.

(String, int) fetchUser() {
  return ('Alice', 42);
}

void main() {
  var user = fetchUser();
  print(user.$1); // Alice
}

Patterns and Pattern Matching

Use patterns to destructure complex data into local variables and match against specific shapes or values. Use them in switch, if-case, or variable declarations to unpack data directly.

Avoid: Manually checking types, nulls, and keys for data extraction.

void processJson(Map<String, dynamic> json) {
  if (json.containsKey('name') && json['name'] is String &&
      json.containsKey('age') && json['age'] is int) {
    String name = json['name'];
    int age = json['age'];
    print('$name is $age years old.');
  }
}