An idea for an extension type for normalized floating point values

normalized_double.dart

/// A value that is guaranteed to be normalized (between `0.0` and `1.0`).
///
/// Might be useful to avoid confusion in math-heavy code.
/// For example, a function might expect some of its arguments
/// to be normalized real numbers. Instead of just documenting
/// it in API docs or checking it at runtime, we can express it
/// through the parameter's static type.
///
/// This is an extension type. The nice thing about those is that
/// they have zero runtime overhead.
extension type NormalizedDouble._(double value) implements double {
  NormalizedDouble(double value)
      : assert(value >= 0),
        assert(value <= 1),
        value = value.clamp(0, 1);
}

extension AsNormalizedDoubleExtension on double {
  /// Asserts that this [double] is a normalized value
  /// (between `0.0` and `1.0`).
  ///
  /// This does _not_ check whether the value is really normalized.
  /// You would normally use this just after a computation.
  NormalizedDouble get asNormalizedDouble => NormalizedDouble._(this);
}