From d7f38bd5cd22205de7848c49c3aba01f17acf96e Mon Sep 17 00:00:00 2001
From: Christopher Armstrong <radix@twistedmatrix.com>
Date: Sat, 23 Dec 2017 13:38:45 -0600
Subject: [PATCH] Implement num::Zero.

Part of #26.
---
 src/system.rs | 19 +++++++++++++++++++
 src/tests.rs  |  8 ++++++++
 2 files changed, 27 insertions(+)

diff --git a/src/system.rs b/src/system.rs
index 92f8d3cd..6e4a8b39 100644
--- a/src/system.rs
+++ b/src/system.rs
@@ -839,6 +839,25 @@ macro_rules! system {
             }
         }
 
+        impl<D, U, V> $crate::num::Zero for Quantity<D, U, V>
+        where
+            D: Dimension + ?Sized,
+            U: Units<V> + ?Sized,
+            V: $crate::num::Num + $crate::Conversion<V>,
+        {
+            fn zero() -> Self {
+                Quantity {
+                    dimension: $crate::lib::marker::PhantomData,
+                    units: $crate::lib::marker::PhantomData,
+                    value: V::zero(),
+                }
+            }
+
+            fn is_zero(&self) -> bool {
+                self.value.is_zero()
+            }
+        }
+
         /// Macro to implement [`quantity`](si/struct.Quantity.html) type aliases for a specific
         /// [system of units][units] and value storage type.
         ///
diff --git a/src/tests.rs b/src/tests.rs
index 734b365c..d5294ae1 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -387,6 +387,14 @@ mod system_macro {
 
         Q!(tests, V);
 
+        #[test]
+        fn zero() {
+            let z = Length::zero();
+
+            Test::assert_eq(z.value, 0.0);
+            assert!(z.is_zero());
+        }
+
         quickcheck! {
             #[allow(trivial_casts)]
             fn from_base(v: A<V>) -> bool