dart-best-practices

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.

When NOT to use (Abstention Guardrails)

Do NOT apply this skill or refactor code when:

• Public API Breaking Changes: Refactoring would alter public API contracts, return types, or parameter signatures in published packages without a coordinated major SemVer bump.
• Dogmatic Micro-Optimizations: Rewriting clear, readable code for negligible theoretical gains (e.g. replacing clear string concatenation in a simple one-line log message with multiline quotes).
• Domain-Specific or Code-Generated Files: Generated files (*.g.dart, *.freezed.dart, protobufs) or files where line lengths and string layouts are managed by code generators.
• Explicit Type Annotations in Public Interfaces: Replacing explicit type annotations with var or final where explicit types document the public API surface or disambiguate complex generics.

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-----''';

Line Length

Avoid lines longer than 80 characters, even in Markdown files and comments. This ensures code is readable in split-screen views and on smaller screens without horizontal scrolling.

Prefer: Target 80 characters for wrapping text. Exceptions are allowed for long URLs or identifiers that cannot be broken.

Discovery

Multi-line Strings

To find candidates for multi-line strings, search for string concatenation with + involving newlines:

• Regex: ['"]\s*\+\s*['"]
• Regex: \+\s*['"].*\\n

Line Length

• Rely on the lines_longer_than_80_chars lint from the analyzer.

Related Skills

• dart-modern-features: For idiomatic usage of modern Dart features like Pattern Matching (useful for deep JSON extraction), Records, and Switch Expressions.