Added comparison operators for cell records.

The will be useful for sorting cell records. Equality and ordering is
defined solely on records IDs.

src/swcio.hpp

@@ -79,18 +79,43 @@ public:
     cell_record(const cell_record &other) = default;
     cell_record &operator=(const cell_record &other) = default;
 
+    // Equality and comparison operators
     friend bool operator==(const cell_record &lhs,
                            const cell_record &rhs)
     {
         return lhs.id_ == rhs.id_;
     }
 
+    friend bool operator<(const cell_record &lhs,
+                          const cell_record &rhs)
+    {
+        return lhs.id_ < rhs.id_;
+    }
+
+    friend bool operator<=(const cell_record &lhs,
+                           const cell_record &rhs)
+    {
+        return (lhs < rhs) || (lhs == rhs);
+    }
+
     friend bool operator!=(const cell_record &lhs,
                            const cell_record &rhs)
     {
         return !(lhs == rhs);
     }
 
+    friend bool operator>(const cell_record &lhs,
+                          const cell_record &rhs)
+    {
+        return !(lhs < rhs) && (lhs != rhs);
+    }
+
+    friend bool operator>=(const cell_record &lhs,
+                           const cell_record &rhs)
+    {
+        return !(lhs < rhs);
+    }
+
     friend std::ostream &operator<<(std::ostream &os, const cell_record &cell);
 
     kind type() const

tests/test_swcio.cpp

@@ -87,6 +87,22 @@ TEST(cell_record, construction)
     }
 }
 
+TEST(cell_record, comparison)
+{
+    using namespace nestmc::io;
+
+    {
+        // check comparison operators
+        cell_record cell0(cell_record::custom, 0, 1., 1., 1., 1., -1);
+        cell_record cell1(cell_record::custom, 0, 2., 3., 4., 5., -1);
+        cell_record cell2(cell_record::custom, 1, 2., 3., 4., 5., -1);
+        EXPECT_EQ(cell0, cell1);
+        EXPECT_LT(cell0, cell2);
+        EXPECT_GT(cell2, cell1);
+    }
+
+}
+
 TEST(swc_parser, invalid_input)
 {
     using namespace nestmc::io;