From d926787965e74290b0ffe30d7443671cfbc06521 Mon Sep 17 00:00:00 2001
From: Maximos Nikiforakis <nikiforos@live.co.uk>
Date: Fri, 16 Feb 2024 08:06:57 +0200
Subject: [PATCH] Introduce aliased_generic_descriptor method in
 AliasMeasurementUnit

---
 src/property_utils/units/descriptors.py | 17 +++++++++++++++++
 src/property_utils/units/units.py       | 10 ++++++++++
 2 files changed, 27 insertions(+)

diff --git a/src/property_utils/units/descriptors.py b/src/property_utils/units/descriptors.py
index 90f9583..82bb338 100644
--- a/src/property_utils/units/descriptors.py
+++ b/src/property_utils/units/descriptors.py
@@ -326,6 +326,9 @@ def from_descriptor(descriptor: UnitDescriptor) -> MeasurementUnit:
         it is intended to be used to convert an unknown unit descriptor to an
         AliasMeasurementUnit.
 
+        Subclasses should implement aliased_generic_descriptor and alias_mapping
+        methods.
+
         Raises WrongUnitDescriptorType if given descriptor cannot be translated
         to an AliasMeasurementUnit  instance.
 
@@ -345,6 +348,20 @@ def from_descriptor(descriptor: UnitDescriptor) -> MeasurementUnit:
             f"cannot create AliasMeasurementUnit from descriptor {descriptor}"
         )
 
+    @classmethod
+    def aliased_generic_descriptor(cls) -> GenericUnitDescriptor:
+        """
+        Implement this method by returning the generic of the unit descriptor that this
+        measurement unit aliases.
+
+        >>> class LengthUnit(MeasurementUnit): ...
+        >>> class AreaUnit(AliasMeasurementUnit):
+        ...     @classmethod
+        ...     def aliased_generic_descriptor(cls):
+        ...         return LengthUnit**2
+        """
+        raise NotImplementedError
+
 
 @dataclass
 class GenericDimension:
diff --git a/src/property_utils/units/units.py b/src/property_utils/units/units.py
index 893219c..d968a13 100644
--- a/src/property_utils/units/units.py
+++ b/src/property_utils/units/units.py
@@ -1,6 +1,8 @@
 from property_utils.units.descriptors import (
     MeasurementUnit,
     AliasMeasurementUnit,
+    GenericCompositeDimension,
+    UnitDescriptor,
 )
 
 
@@ -57,6 +59,10 @@ class PressureUnit(AliasMeasurementUnit):
     PASCAL = "Pa"
     KILO_PASCAL = "kPa"
 
+    @classmethod
+    def aliased_generic_descriptor(cls) -> GenericCompositeDimension:
+        return MassUnit / LengthUnit / (TimeUnit**2)
+
 
 class EnergyUnit(AliasMeasurementUnit):
     JOULE = "J"
@@ -66,3 +72,7 @@ class EnergyUnit(AliasMeasurementUnit):
     CALORIE = "cal"
     KILO_CALORIE = "kcal"
     BTU = "Btu"
+
+    @classmethod
+    def aliased_generic_descriptor(cls) -> GenericCompositeDimension:
+        return MassUnit * (LengthUnit**2) / (TimeUnit**2)