counters: base counter_id on utils::tagged_uuid

Use the common base class for uuid-based types.

tagged_uuid::to_uuid defined here for backward
compatibility, but it will be renamed in the next patch
to uuid().

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>

counters.cc

@@ -12,10 +12,6 @@
 
 #include <boost/range/algorithm/sort.hpp>
 
-std::ostream& operator<<(std::ostream& os, const counter_id& id) {
-    return os << id.to_uuid();
-}
-
 std::ostream& operator<<(std::ostream& os, counter_shard_view csv) {
     return os << "{global_shard id: " << csv.id() << " value: " << csv.value()
               << " clock: " << csv.logical_clock() << "}";

counters.hh

@@ -18,45 +18,17 @@
 class mutation;
 class atomic_cell_or_collection;
 
-class counter_id {
-    int64_t _least_significant;
-    int64_t _most_significant;
+class counter_id : public utils::tagged_uuid<counter_id> {
 public:
-    static_assert(std::is_same<decltype(std::declval<utils::UUID>().get_least_significant_bits()), int64_t>::value
-            &&  std::is_same<decltype(std::declval<utils::UUID>().get_most_significant_bits()), int64_t>::value,
-        "utils::UUID is expected to work with two signed 64-bit integers");
-
     counter_id() = default;
-    explicit counter_id(utils::UUID uuid) noexcept
-        : _least_significant(uuid.get_least_significant_bits())
-        , _most_significant(uuid.get_most_significant_bits())
-    { }
+    explicit counter_id(utils::UUID uuid) noexcept : utils::tagged_uuid<counter_id>(uuid) {}
 
-    utils::UUID to_uuid() const {
-        return utils::UUID(_most_significant, _least_significant);
-    }
-
-    bool operator<(const counter_id& other) const {
-        return to_uuid() < other.to_uuid();
-    }
-    bool operator>(const counter_id& other) const {
-        return other.to_uuid() < to_uuid();
-    }
-    bool operator==(const counter_id& other) const {
-        return to_uuid() == other.to_uuid();
-    }
-    bool operator!=(const counter_id& other) const {
-        return !(*this == other);
-    }
-public:
     // For tests.
     static counter_id generate_random() {
         return counter_id(utils::make_random_uuid());
     }
 };
 
-std::ostream& operator<<(std::ostream& os, const counter_id& id);
-
 template<mutable_view is_mutable>
 class basic_counter_shard_view {
     enum class offset : unsigned {

utils/UUID.hh

@@ -217,6 +217,15 @@ struct tagged_uuid {
     bool operator<(const tagged_uuid& o) const noexcept {
         return id < o.id;
     }
+    bool operator>(const tagged_uuid& o) const noexcept {
+        return id > o.id;
+    }
+    bool operator<=(const tagged_uuid& o) const noexcept {
+        return id <= o.id;
+    }
+    bool operator>=(const tagged_uuid& o) const noexcept {
+        return id >= o.id;
+    }
     explicit operator bool() const noexcept {
         // The default constructor sets the id to nil, which is
         // guaranteed to not match any valid id.
@@ -225,6 +234,11 @@ struct tagged_uuid {
     static tagged_uuid create_random_id() noexcept { return tagged_uuid{utils::make_random_uuid()}; }
     explicit tagged_uuid(const utils::UUID& uuid) noexcept : id(uuid) {}
     tagged_uuid() = default;
+
+    // FIXME: rename to uuid()
+    const utils::UUID& to_uuid() const noexcept {
+        return id;
+    }
 };
 } // namespace utils