Dart Best Practices

1. When to use this skill

Use this skill when:

• Writing or reviewing Dart code.
• Looking for guidance on idiomatic Dart usage.

2. Best Practices

Multi-line Strings

Prefer using multi-line strings (''') over concatenating strings with + and \n, especially for large blocks of text like SQL queries, HTML, or PEM-encoded keys. This improves readability and avoids lines_longer_than_80_chars lint errors by allowing natural line breaks.

Avoid:

final pem = '-----BEGIN RSA PRIVATE KEY-----\n' +
    base64Encode(fullBytes) +
    '\n-----END RSA PRIVATE KEY-----';

Prefer:

final pem = '''
-----BEGIN RSA PRIVATE KEY-----
${base64Encode(fullBytes)}
-----END RSA PRIVATE KEY-----''';

Robust JSON Parsing with Switch Expressions

When implementing fromJson factory constructors or parsing untrusted Map<String, dynamic> input, use switch expressions for type validation and extraction. This is more readable than manual is checks and cleaner than unsafe casts (as).

Avoid (Unsafe Access):

final json = jsonDecode(stdout);
if (json is Map &&
    json['configuration'] is Map &&
    json['configuration']['properties'] is Map &&
    json['configuration']['properties']['core'] is Map) {
  return json['configuration']['properties']['core']['project'] as String?;
}
return null;

Prefer (Deep Pattern Matching):

return switch (jsonDecode(stdout)) {
  {
    'configuration': {
      'properties': {'core': {'project': final String project}},
    },
  } =>
    project,
  _ => null,
};

This pattern ensures that missing or incorrect types are caught with descriptive errors rather than opaque runtime exceptions.