isSI and isMetric getters on unit

CHANGELOG.md

@@ -9,6 +9,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+* Added `Unit.isSI`, returning `true` only for the actual SI unit of each quantity family (e.g. `LengthUnit.meter`, `MassUnit.kilogram`, `TimeUnit.second`). Logarithmic and non-SI-only families (`LevelRatio`, `PowerLevel`, `VoltageLevel`, `SoundPressureLevel`, `FuelConsumption`, `Information`) always return `false`.
+* Added `Unit.isMetric`, returning `true` for units that are part of the metric system (including non-SI metric units like `LengthUnit.kilometer`, `MassUnit.tonne`, `VolumeUnit.litre`, and `TemperatureUnit.celsius`), and `false` for imperial/US customary, nautical, astronomical, CGS, and other non-metric units. Purely logarithmic ratio families (`LevelRatio`, `PowerLevel`, `VoltageLevel`, `SoundPressureLevel`) always return `false`.
 * Added `EnergyDensity`, a new linear quantity for energy per unit volume (dimensionally equivalent to `Pressure`), supporting `J/m³`, `J/L`, and `Wh/L`, with `EnergyDensity.from(Energy, Volume)`, `energyOf(Volume)`, and `volumeFor(Energy)` dimensional-analysis helpers, plus a granular `energy_density.dart` entry point.
 * Added the `VolumetricFlowRate` linear quantity (`m³/s`, `m³/min`, `m³/h`, `L/s`, `L/min`, `L/h`, `mL/min`, `ft³/s`, `ft³/min`, `gal/min`, `gal/h`), with `VolumetricFlowRate.from(Volume, Time)`, `volumeOver(Time)`, and `timeFor(Volume)` dimensional-analysis bridges.
 * Added a granular entry point for the new family: `volumetric_flow_rate.dart`.

lib/src/core/unit.dart

@@ -12,6 +12,13 @@ abstract class Unit<T extends Unit<T>> {
 
   /// A human-readable symbol or abbreviation for the unit.
   String get symbol;
+
+  /// Returns `true` if this unit is part of the International System of Units (SI).
+  /// if the unit is SI derived, this will return `true` only for the base unit of that dimension.
+  bool get isSI;
+
+  /// Indicates whether the unit is part of the metric system.
+  bool get isMetric;
 }
 
 /// A contract for units that scale linearly (via a simple multiplier).

lib/src/units/acceleration/acceleration_unit.dart

@@ -107,6 +107,22 @@ enum AccelerationUnit implements LinearUnit<AccelerationUnit> {
   @override
   final String symbol;
 
+  /// Returns `true` only for [meterPerSecondSquared], the SI derived unit of acceleration.
+  @override
+  bool get isSI => this == AccelerationUnit.meterPerSecondSquared;
+
+  /// Returns `true` only for [meterPerSecondSquared],
+  /// [centimeterPerSecondSquared], and [kilometerPerHourPerSecond]; `false`
+  /// for the imperial/nautical units and the physical constant
+  /// [standardGravity].
+  @override
+  bool get isMetric => switch (this) {
+    AccelerationUnit.meterPerSecondSquared ||
+    AccelerationUnit.centimeterPerSecondSquared ||
+    AccelerationUnit.kilometerPerHourPerSecond => true,
+    _ => false,
+  };
+
   // --- Pre-calculated direct conversion factors ---
   final double _factorToMeterPerSecondSquared;
   final double _factorToStandardGravity;

lib/src/units/angle/angle_unit.dart

@@ -57,6 +57,19 @@ enum AngleUnit implements LinearUnit<AngleUnit> {
   @override
   final String symbol;
 
+  /// Returns `true` only for [radian], the SI derived unit of plane angle.
+  @override
+  bool get isSI => this == AngleUnit.radian;
+
+  /// Returns `true` only for [radian], [milliradian], and [gradian] (the
+  /// decimal metric angle unit); `false` for [degree], [revolution],
+  /// [arcminute], and [arcsecond], which are sexagesimal/non-decimal units.
+  @override
+  bool get isMetric => switch (this) {
+    AngleUnit.radian || AngleUnit.milliradian || AngleUnit.gradian => true,
+    _ => false,
+  };
+
   // --- Pre-calculated direct conversion factors from this unit to all others ---
   final double _factorToRadian;
   final double _factorToDegree;

lib/src/units/angular_velocity/angular_velocity_unit.dart

@@ -65,6 +65,16 @@ enum AngularVelocityUnit implements LinearUnit<AngularVelocityUnit> {
   @override
   final String symbol;
 
+  /// Returns `true` only for [radianPerSecond], the SI derived unit of angular velocity.
+  @override
+  bool get isSI => this == AngularVelocityUnit.radianPerSecond;
+
+  /// Returns `true` only for [radianPerSecond]; `false` for [degreePerSecond],
+  /// [revolutionPerMinute], and [revolutionPerSecond], which are not decimal
+  /// metric units.
+  @override
+  bool get isMetric => this == AngularVelocityUnit.radianPerSecond;
+
   // --- Pre-calculated direct conversion factors ---
   final double _factorToRadianPerSecond;
   final double _factorToDegreePerSecond;

lib/src/units/area/area_unit.dart

@@ -80,6 +80,22 @@ enum AreaUnit implements LinearUnit<AreaUnit> {
   @override
   final String symbol;
 
+  /// Returns `true` only for [squareMeter], the SI derived unit of area.
+  @override
+  bool get isSI => this == AreaUnit.squareMeter;
+
+  /// Returns `false` for imperial/US customary land-area units; `true` for
+  /// all decimal metric units (including [hectare]).
+  @override
+  bool get isMetric => switch (this) {
+    AreaUnit.squareInch ||
+    AreaUnit.squareFoot ||
+    AreaUnit.squareYard ||
+    AreaUnit.squareMile ||
+    AreaUnit.acre => false,
+    _ => true,
+  };
+
   // --- Pre-calculated direct conversion factors ---
   final double _factorToSquareMeter;
   final double _factorToSquareDecimeter;

lib/src/units/current/current_unit.dart

@@ -80,6 +80,18 @@ enum CurrentUnit implements LinearUnit<CurrentUnit> {
   @override
   final String symbol;
 
+  /// Returns `true` only for [ampere], the SI base unit of electric current.
+  @override
+  bool get isSI => this == CurrentUnit.ampere;
+
+  /// Returns `false` for the CGS units [statampere] and [abampere];
+  /// `true` for all decimal metric units.
+  @override
+  bool get isMetric => switch (this) {
+    CurrentUnit.statampere || CurrentUnit.abampere => false,
+    _ => true,
+  };
+
   // --- Pre-calculated direct conversion factors from this unit to all others ---
   final double _factorToAmpere;
   final double _factorToMilliampere;

lib/src/units/density/density_unit.dart

@@ -58,6 +58,15 @@ enum DensityUnit implements LinearUnit<DensityUnit> {
   @override
   final String symbol;
 
+  /// Returns `true` only for [kilogramPerCubicMeter], the SI derived unit of density.
+  @override
+  bool get isSI => this == DensityUnit.kilogramPerCubicMeter;
+
+  /// Returns `true` for all units, since every `DensityUnit` member is a
+  /// decimal metric unit.
+  @override
+  bool get isMetric => true;
+
   // --- Pre-calculated direct conversion factors ---
   final double _factorToKilogramPerCubicMeter;
   final double _factorToGramPerCubicCentimeter;

lib/src/units/electric_charge/electric_charge_unit.dart

@@ -69,6 +69,22 @@ enum ElectricChargeUnit implements LinearUnit<ElectricChargeUnit> {
   @override
   final String symbol;
 
+  /// Returns `true` only for [coulomb], the SI derived unit of electric charge.
+  @override
+  bool get isSI => this == ElectricChargeUnit.coulomb;
+
+  /// Returns `false` for the physics-constant [elementaryCharge] and the CGS
+  /// units [statcoulomb], [franklin], and [abcoulomb]; `true` for all decimal
+  /// metric units (including [ampereHour]).
+  @override
+  bool get isMetric => switch (this) {
+    ElectricChargeUnit.elementaryCharge ||
+    ElectricChargeUnit.statcoulomb ||
+    ElectricChargeUnit.franklin ||
+    ElectricChargeUnit.abcoulomb => false,
+    _ => true,
+  };
+
   // --- Pre-calculated direct conversion factors ---
   final double _factorToCoulomb;
   final double _factorToKilocoulomb;

lib/src/units/energy/energy_unit.dart

@@ -95,6 +95,19 @@ enum EnergyUnit implements LinearUnit<EnergyUnit> {
   @override
   final String symbol;
 
+  /// Returns `true` only for [joule], the SI derived unit of energy.
+  @override
+  bool get isSI => this == EnergyUnit.joule;
+
+  /// Returns `false` for the physics-constant [electronvolt] and the
+  /// imperial [btu]; `true` for all decimal metric units (including
+  /// [calorie] and [wattHour] families).
+  @override
+  bool get isMetric => switch (this) {
+    EnergyUnit.electronvolt || EnergyUnit.btu => false,
+    _ => true,
+  };
+
   // --- Pre-calculated direct conversion factors from this unit to all others ---
   final double _factorToJoule;
   final double _factorToMillijoule;

lib/src/units/force/force_unit.dart

@@ -68,6 +68,19 @@ enum ForceUnit implements LinearUnit<ForceUnit> {
   @override
   final String symbol;
 
+  /// Returns `true` only for [newton], the SI derived unit of force.
+  @override
+  bool get isSI => this == ForceUnit.newton;
+
+  /// Returns `false` for the imperial [poundForce] and [poundal], and the
+  /// CGS [dyne]; `true` for all decimal metric units (including the
+  /// gravitational metric units [kilogramForce] and [gramForce]).
+  @override
+  bool get isMetric => switch (this) {
+    ForceUnit.poundForce || ForceUnit.dyne || ForceUnit.poundal => false,
+    _ => true,
+  };
+
   // --- Pre-calculated direct conversion factors ---
   final double _factorToNewton;
   final double _factorToNanonewton;

lib/src/units/frequency/frequency_unit.dart

@@ -60,6 +60,21 @@ enum FrequencyUnit implements LinearUnit<FrequencyUnit> {
   @override
   final String symbol;
 
+  /// Returns `true` only for [hertz], the SI derived unit of frequency.
+  @override
+  bool get isSI => this == FrequencyUnit.hertz;
+
+  /// Returns `false` for [revolutionsPerMinute], [beatsPerMinute], and
+  /// [degreePerSecond], which are not decimal metric units; `true` for all
+  /// SI-prefixed hertz units and [radianPerSecond].
+  @override
+  bool get isMetric => switch (this) {
+    FrequencyUnit.revolutionsPerMinute ||
+    FrequencyUnit.beatsPerMinute ||
+    FrequencyUnit.degreePerSecond => false,
+    _ => true,
+  };
+
   // --- Pre-calculated direct conversion factors ---
   final double _factorToHertz;
   final double _factorToTerahertz;

lib/src/units/fuel_consumption/fuel_consumption_unit.dart

@@ -26,6 +26,17 @@ enum FuelConsumptionUnit implements Unit<FuelConsumptionUnit> {
   @override
   final String symbol;
 
+  /// None of these fuel-economy units are part of the SI, so this always
+  /// returns `false`.
+  @override
+  bool get isSI => false;
+
+  /// Returns `true` only for [litersPer100Km] and [kilometerPerLiter], the
+  /// metric fuel-consumption units; `false` for [mpgUs] and [mpgUk].
+  @override
+  bool get isMetric =>
+      this == FuelConsumptionUnit.litersPer100Km || this == FuelConsumptionUnit.kilometerPerLiter;
+
   /// Unit symbols matched strictly case-sensitive.
   ///
   /// Note: The unqualified abbreviation `mpg` defaults to US gallons.

lib/src/units/information/information_unit.dart

@@ -147,6 +147,27 @@ enum InformationUnit implements LinearUnit<InformationUnit> {
   @override
   final String symbol;
 
+  /// The SI does not define a unit for digital information, so this always
+  /// returns `false`, even for units that use SI decimal prefixes (e.g. [kilobit]).
+  @override
+  bool get isSI => false;
+
+  /// Returns `false` for the IEC/binary units ([kibibyte] through
+  /// [yobibyte]), which use binary (base-2) prefixes; `true` for [bit],
+  /// [byte], and all SI/decimal-prefixed bit and byte units.
+  @override
+  bool get isMetric => switch (this) {
+    InformationUnit.kibibyte ||
+    InformationUnit.mebibyte ||
+    InformationUnit.gibibyte ||
+    InformationUnit.tebibyte ||
+    InformationUnit.pebibyte ||
+    InformationUnit.exbibyte ||
+    InformationUnit.zebibyte ||
+    InformationUnit.yobibyte => false,
+    _ => true,
+  };
+
   // --- Pre-calculated direct conversion factors from this unit to all others ---
   final double _factorToBit;
   final double _factorToByte;

lib/src/units/length/length_unit.dart

@@ -119,6 +119,25 @@ enum LengthUnit implements LinearUnit<LengthUnit> {
   @override
   final String symbol;
 
+  /// Returns `true` only for [meter], the SI base unit of length.
+  @override
+  bool get isSI => this == LengthUnit.meter;
+
+  /// Returns `false` for imperial/US customary, nautical, and astronomical
+  /// units; `true` for all decimal metric units (including [angstrom]).
+  @override
+  bool get isMetric => switch (this) {
+    LengthUnit.inch ||
+    LengthUnit.foot ||
+    LengthUnit.yard ||
+    LengthUnit.mile ||
+    LengthUnit.nauticalMile ||
+    LengthUnit.astronomicalUnit ||
+    LengthUnit.lightYear ||
+    LengthUnit.parsec => false,
+    _ => true,
+  };
+
   // --- Pre-calculated direct conversion factors from this unit to all others ---
   final double _factorToMeter;
   final double _factorToKilometer;

lib/src/units/level_ratio/level_ratio_unit.dart

@@ -23,6 +23,16 @@ enum LevelRatioUnit implements LinearUnit<LevelRatioUnit> {
   @override
   final String symbol;
 
+  /// The decibel and neper are non-SI units accepted for use with the SI,
+  /// but neither is itself an SI unit, so this always returns `false`.
+  @override
+  bool get isSI => false;
+
+  /// Returns `false` for all units, since logarithmic ratio units are not
+  /// tied to any unit system.
+  @override
+  bool get isMetric => false;
+
   final double _factorToDecibel;
   final double _factorToNeper;
 

lib/src/units/luminous/luminous_intensity_unit.dart

@@ -92,6 +92,15 @@ enum LuminousIntensityUnit implements LinearUnit<LuminousIntensityUnit> {
   @override
   final String symbol;
 
+  /// Returns `true` only for [candela], the SI base unit of luminous intensity.
+  @override
+  bool get isSI => this == LuminousIntensityUnit.candela;
+
+  /// Returns `true` for all units, since every `LuminousIntensityUnit` member
+  /// is a decimal metric (SI-prefixed) unit.
+  @override
+  bool get isMetric => true;
+
   // --- Pre-calculated direct conversion factors from this unit to all others ---
   final double _factorToCandela;
   final double _factorToMillicandela;

lib/src/units/mass/mass_unit.dart

@@ -117,6 +117,25 @@ enum MassUnit implements LinearUnit<MassUnit> {
   @override
   final String symbol;
 
+  /// Returns `true` only for [kilogram], the SI base unit of mass.
+  @override
+  bool get isSI => this == MassUnit.kilogram;
+
+  /// Returns `false` for imperial/US customary units and the physics-constant
+  /// [atomicMassUnit]; `true` for all decimal metric units (including [tonne]
+  /// and [carat]).
+  @override
+  bool get isMetric => switch (this) {
+    MassUnit.pound ||
+    MassUnit.ounce ||
+    MassUnit.stone ||
+    MassUnit.slug ||
+    MassUnit.shortTon ||
+    MassUnit.longTon ||
+    MassUnit.atomicMassUnit => false,
+    _ => true,
+  };
+
   // --- Pre-calculated direct conversion factors from this unit to all others ---
   final double _factorToKilogram;
   final double _factorToHectogram;

lib/src/units/molar/molar_unit.dart

@@ -108,6 +108,15 @@ enum MolarUnit implements LinearUnit<MolarUnit> {
   @override
   final String symbol;
 
+  /// Returns `true` only for [mole], the SI base unit for amount of substance.
+  @override
+  bool get isSI => this == MolarUnit.mole;
+
+  /// Returns `false` only for the imperial [poundMole]; `true` for all
+  /// decimal metric units.
+  @override
+  bool get isMetric => this != MolarUnit.poundMole;
+
   // --- Pre-calculated direct conversion factors from this unit to all others ---
   // These are calculated once in the const constructor for performance.
 

lib/src/units/power/power_unit.dart

@@ -74,6 +74,19 @@ enum PowerUnit implements LinearUnit<PowerUnit> {
   @override
   final String symbol;
 
+  /// Returns `true` only for [watt], the SI derived unit of power.
+  @override
+  bool get isSI => this == PowerUnit.watt;
+
+  /// Returns `false` for the imperial [horsepower] and [btuPerHour], and the
+  /// CGS [ergPerSecond]; `true` for all SI-prefixed watt units and
+  /// [metricHorsepower].
+  @override
+  bool get isMetric => switch (this) {
+    PowerUnit.horsepower || PowerUnit.btuPerHour || PowerUnit.ergPerSecond => false,
+    _ => true,
+  };
+
   // --- Pre-calculated direct conversion factors ---
   final double _factorToWatt;
   final double _factorToNanowatt;