dart-optimization

name	dart-optimization
description	Optimize Dart code for performance, type safety, and runtime error prevention. Use when profiling hot paths, enforcing sound typing, handling null safety, or debugging type mismatches and runtime failures.
metadata	{"platforms":"dart","languages":"dart","category":"optimization"}

Optimization & Debugging

Performance in Dart goes beyond UI rendering; it's about efficient execution, smart resource utilization, and sound error handling.

Dart Performance Patterns

• Standardize Types: Avoid dynamic. Use explicit types or Object?. Statically typed code allows the compiler to perform far better optimizations.
• Efficient Collections:
  • Use Set for average O(1) containment checks.
  • Use List for ordered indexing.
  • Prefer Iterable methods (map, where) for readability, but use for loops in performance-critical hot paths.
• Inlining: Small getters and trivial functions are often inlined by the VM/AOT, but keeping them simple ensures this optimization happens.

Compile-Time Optimizations

• Final & Const: Declare variables as final whenever possible. Use const constructors for widgets and data models to enable compile-time allocation and reduce runtime garbage collection pressure.
• Ternary vs If-Else: In Dart, they are generally equivalent, but prioritize readability. Use switch expressions (Dart 3+) for exhaustive and efficient pattern matching.
• Extension Types: Use Dart 3.3+ extension type zero-cost abstractions for type wrapping to eliminate runtime allocation overhead (see dart-modern-syntax).
• Private Named Parameters: Use Dart 3.12+ MyClass({this._privateField}) constructors to eliminate initializer list code boilerplate (see dart-modern-syntax).

Hot Paths & Loops

• Minimize Work in Loops: Extract calculations and object creations outside of loops.
• Collection Literals: Use literal syntax [] or {} instead of constructors like List() for brevity and minor performance gains.

Type System & Soundness

Enforce Dart's sound type system to prevent runtime invalid states.

• Method Overrides: Maintain sound return types (covariant) and parameter types (contravariant). Never tighten a parameter type in a subclass unless explicitly marked with the covariant keyword.
• Generics & Collections: Add explicit type annotations to generic classes (e.g., List<T>). Never assign a List<dynamic> to a typed list.
• Downcasting: Avoid implicit downcasts from dynamic. Use explicit casts (e.g., as List<Cat>) when necessary, but ensure the underlying runtime type matches to prevent TypeError exceptions.
• Strict Casts: Enable strict-casts: true in analysis_options.yaml to force explicit casting and catch implicit downcast errors at compile time.

Null Safety & Error Handling

Eliminate static errors related to null safety by correctly managing variable initialization and nullability.

• Modifiers: Apply ? for nullable types, ! for null assertions, and required for named parameters that cannot be null.
• Late Initialization: Use the late keyword for non-nullable variables guaranteed to be initialized before use.
• Catching: Catch Exception subtypes for recoverable failures.
• Errors: Never explicitly catch Error or its subtypes (e.g., TypeError, ArgumentError). Errors indicate programming bugs that must be fixed, not caught.
• Rethrowing: Use rethrow inside a catch block to propagate an exception while preserving its original stack trace.

Profiling & Debugging

• DevTools CPU Profiler: Identify hot paths and "heavy" functions.
• Benchmarking: Use package:benchmark_harness for scientific performance measurement of non-UI logic.
• Hot Reload vs Restart: Use hot reload for UI changes. For state initialization or deep logic changes that cause runtime errors, use hot restart to clear the state tree.