cast0r — Safe try/as and transform extension that works on any object for Dart

castor_safe_try_as.dart

/// Cast Or provide default value (optional or safely defaulted)
/// by the way, "castor" is the french word for beaver...
/// ```
///           ___
///          /. .\
///         =\_t_/=
///           [|]
/// ```
///
extension CastOrExtension<T extends Object> on T {
  /// Safely cast anything :
  ///
  /// ```dart
  /// null.tryAs<int>()?.isFinite; // stupid but fine...
  /// null.tryAs<int>((val) => 34)?.isFinite; // stupid but fine...
  /// null.tryAs<int>((val) => val ?? 34)?.isFinite; // stupid but fine...
  /// ```
  ///
  B? tryCast<B extends T>([B? Function(T? val)? transform]) {
    final that = this;
    final valueTransformer = transform ?? (val) => that is B ? that : null;
    try {
      return valueTransformer(that);
    } catch (_) {
      // guard anything
      return null;
    }
  }

  /// It worth mentionning that [castOr] can provide a complete other type than
  /// the original one, for example :
  /// ```dart
  /// "String".as<List<String?>>((val) => [val]); => List<String?> => ["String"]
  /// ```
  B castOr<B>(B Function(T? val) transform) {
    final that = this;
    if (that is B) {
      return that as B;
    } else {
      return transform(that);
    }
  }
}

final _samples = [
  null,
  33,
  "myString",
  [33, "myString"]
];

final _samplers = <String, Object? Function(Object? T)>{
  '`dynamic` keyword is Bad bad bad not good': (dynamic object) {
    try {
      // will fail :(
      return object.tryAs<Object?>();
    } catch (e) {
      return 'Ooooh myyy. Dynamic is sh**t :(';
    }
  },
  'Is null?': (object) {
    return (object?.tryCast() == null);
  },
  'Unnecessary type check': (object) {
    // ignore: unnecessary_type_check
    return object?.tryCast<String>() is String?;
  },
  "Expect an isFinite <int>": (object) {
    return object?.tryCast<int>()?.tryCast()?.isFinite;
  },
  "Expect an alternative of the same type if null": (object) {
    return object?.tryCast<int>()?.isFinite;
  },
  "Try an alternative casting": (object) {
    return object
        ?.tryCast<int>((val) => val is double ? val.toInt() : 34)
        ?.isFinite;
  },
  "Fetch an alternative an alternative of the same type if null": (object) {
    return object?.tryCast<int>((val) => 34)?.isFinite;
  },
  "Alternative with the alternate syntax and providing a default": (object) {
    return object
        ?.castOr<int>((that) => 43)
        // not now we now that `u` is `int` as inferred
        .castOr((u) => u?.isOdd ?? true ? 54 : 45)
        .isFinite;
  },
  "Providing a complete other value A.K.A transform": (object) {
    return object
        // map this value into a Set of int
        ?.castOr<Set<int>>((val) => {val is int ? val : 43})
        // and fetch it back as an int
        .castOr<int>((val) => val?.toList().elementAtOrNull(0) ?? 34)
        // you can provide mostly any transformation there
        .isFinite;
  },
};

void main() {
  print("");
  for (final takeThat in _samples) {
    print("Received that one : ${takeThat.runtimeType} —> $takeThat");
    print("——");
    int i = 0;
    for (final sampler in _samplers.entries) {
      print(' ${++i}) ${sampler.key}: ${sampler.value(takeThat)}');
    }
    print("");
  }
}


/// ```
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/// credits : https://textart.sh/topic/beaver