dartlisted

# Dart Standards ## Priority: P0 — Language Correctness ### Null Safety - Avoid `!`. Prefer local promotion, null-check patterns, and private `final` fields. - Use `!` only for documented invariants or framework/external boundaries where non-null is guaranteed but not expressible to the analyzer. - Prefer `?.`, `??`, and null-aware patterns over forced unwrapping. - `AVOID late` if you need to check whether the variable was initialised — use nullable + null-check instead. - `DON'T` explicitly initialise variables to `null`; let the type system express optionality. ### Immutability - Use `const` > `final` > `var`. Use `@freezed` for data classes. - Prefer `final` for all class members. Use `var` only for locally-obvious short-lived locals. - `AVOID` public `late final` fields without initializers. ### Pattern Matching (Dart 3.x) Use `switch` expressions with exhaustive patterns and destructuring. Supported pattern types: | Pattern | Example | |---|---| | Constant | `case 42:` | | Variable | `case var x:` | | Wildcard | `case _:` | | Object | `case Circle(radius: var r):` | | Record | `case (String name, int age):` | | List | `case [first, ...rest]:` | | Map | `case {'key': var v}:` | | Logical-or | `case 1 || 2:` | | Guard | `case var x when x > 0:` | ```dart String describe(Shape s) => switch (s) { Circle(radius: var r) when r > 10 => 'large circle', Circle(radius: var r) => 'circle r=$r', Rectangle(width: var w, height: var h) => '${w}x$h rect', }; ``` ### Recor