Test for std.range.Zip.save

std/range/package.d

@@ -4423,6 +4423,27 @@ pure unittest
     auto zz = z.save;
 }
 
+@safe pure unittest
+{
+    import std.typecons : tuple;
+
+    static class RefRange
+    {
+        @safe: pure:
+        this(int front){ this.front = front; }
+        int front;
+        enum empty = false;
+        void popFront(){ front++; }
+        RefRange save(){ return new RefRange(front); }
+    }
+
+    auto z1 = zip(new RefRange(0), new RefRange(1));
+    auto z2 = z1.save;
+    z1.popFront();
+    assert(z1.front == tuple(1,2));
+    assert(z2.front == tuple(0,1));
+}
+
 /*
     Generate lockstep's opApply function as a mixin string.
     If withIndex is true prepend a size_t index to the delegate.