From 6e4fa6e4738d450451372f00bab2d39160957681 Mon Sep 17 00:00:00 2001
From: Jordan Brauer <jbrauer.inc@gmail.com>
Date: Wed, 2 Oct 2019 16:09:35 -0500
Subject: [PATCH 1/2] add variant property as well as cache registry key for
 current instance

---
 src/UnitConverter/Unit/AbstractUnit.php | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/src/UnitConverter/Unit/AbstractUnit.php b/src/UnitConverter/Unit/AbstractUnit.php
index 409a6fff..1bf5a310 100644
--- a/src/UnitConverter/Unit/AbstractUnit.php
+++ b/src/UnitConverter/Unit/AbstractUnit.php
@@ -69,14 +69,30 @@ abstract class AbstractUnit implements UnitInterface
      */
     protected $value;
 
+    /**
+     * The variant (or "flavour") of the current unit instance. This determines
+     * it's amount of units and is meant to be used for
+     *
+     * @var string
+     */
+    protected $variant;
+
+    /**
+     * A cached version of the unit instance's registry key.
+     *
+     * @var string
+     */
+    private $cachedRegistryKey;
+
     /**
      * Public constructor function for units of measurement.
      *
      * @param int|float|string $value The amount of units to be reprsented by the final object as.
      */
-    public function __construct($value = 1)
+    public function __construct($value = 1, ?string $variant = null)
     {
         $this->value = $value;
+        $this->variant = $variant;
         $this->formulae = [];
 
         $this->configure();
@@ -158,7 +174,12 @@ public function getName(): ?string
 
     public function getRegistryKey(): ?string
     {
-        return $this->unitOf.'.'.$this->symbol;
+        return $this->cachedRegistryKey
+            ?? $this->cachedRegistryKey = implode('.', array_filter([
+                $this->unitOf,
+                $this->symbol,
+                $this->variant,
+            ]));
     }
 
     public function getScientificSymbol(): ?string

From e81657d42579cffef2e53652465fe15278f38283 Mon Sep 17 00:00:00 2001
From: Jordan Brauer <jbrauer.inc@gmail.com>
Date: Wed, 2 Oct 2019 16:10:07 -0500
Subject: [PATCH 2/2] throw some exceptions for when variants are present but
 no selection is given

---
 src/UnitConverter/Registry/UnitRegistry.php | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/UnitConverter/Registry/UnitRegistry.php b/src/UnitConverter/Registry/UnitRegistry.php
index 16e0ab5a..023b134c 100644
--- a/src/UnitConverter/Registry/UnitRegistry.php
+++ b/src/UnitConverter/Registry/UnitRegistry.php
@@ -14,6 +14,7 @@
 
 namespace UnitConverter\Registry;
 
+use RuntimeException;
 use UnitConverter\Exception\BadMeasurement;
 use UnitConverter\Exception\BadRegistry;
 use UnitConverter\Measure;
@@ -64,6 +65,10 @@ public function isUnitRegistered(string $symbol): bool
     {
         foreach ($this->store as $measurement => $units) {
             if (array_key_exists($symbol, $units)) {
+                if (is_array($units[$symbol])) {
+                    throw new RuntimeException(sprintf('Encountered unit "%s" with variants: %s; but have no way to select one', $symbol, implode(', ', array_keys($units[$symbol]))));
+                }
+
                 return true;
             }
         }