Refactor[BMQT]: turn copy operator for Subscription explicit

Signed-off-by: Evgeny Malygin <emalygin@bloomberg.net>

src/groups/bmq/bmqt/bmqt_subscription.h

@@ -203,9 +203,19 @@ class Subscription {
 
     /// Create a new Subscription by copying values from the specified
     /// `other`.
-    Subscription(const Subscription& other);
+    explicit Subscription(const Subscription& other);
 
     // MANIPULATORS
+    /// Assign to this object the value of the specified `rhs` object.
+    Subscription& operator=(const Subscription& rhs);
+
+#if defined(BSLS_COMPILERFEATURES_SUPPORT_RVALUE_REFERENCES) &&               \
+    defined(BSLS_COMPILERFEATURES_SUPPORT_NOEXCEPT)
+    /// Assign to this object the value of the specified `rhs` object.
+    /// After performing this action, the `rhs` object will be left in a
+    /// valid, but unspecified state.
+    Subscription& operator=(Subscription&& rhs);
+#endif
 
     /// Set the maxUnconfirmedMessages to the specified `value`.  The
     /// behavior is undefined unless `value >= 0`. If the specified `value`
@@ -276,9 +286,9 @@ bsl::ostream& operator<<(bsl::ostream& stream, const Subscription& rhs);
 //                             INLINE DEFINITIONS
 // ============================================================================
 
-// ----------------------
+// -------------------------
 // class Subscription_Handle
-// ----------------------
+// -------------------------
 
 inline SubscriptionHandle::SubscriptionHandle()
 : d_id(k_INVALID_HANDLE_ID)
@@ -385,9 +395,9 @@ inline bsl::ostream& SubscriptionExpression::print(bsl::ostream& stream,
     return stream;
 }
 
-// ----------------------
+// ------------------
 // class Subscription
-// ----------------------
+// ------------------
 
 inline Subscription::Subscription()
 : d_maxUnconfirmedMessages()
@@ -428,6 +438,27 @@ Subscription::print(bsl::ostream& stream, int level, int spacesPerLevel) const
 }
 
 // MANIPULATORS
+inline Subscription& Subscription::operator=(const Subscription& rhs)
+{
+    d_maxUnconfirmedMessages = rhs.d_maxUnconfirmedMessages;
+    d_maxUnconfirmedBytes    = rhs.d_maxUnconfirmedBytes;
+    d_consumerPriority       = rhs.d_consumerPriority;
+    d_expression             = rhs.d_expression;
+    return *this;
+}
+
+#if defined(BSLS_COMPILERFEATURES_SUPPORT_RVALUE_REFERENCES) &&               \
+    defined(BSLS_COMPILERFEATURES_SUPPORT_NOEXCEPT)
+inline Subscription& Subscription::operator=(Subscription&& rhs)
+{
+    d_maxUnconfirmedMessages = bsl::move(rhs.d_maxUnconfirmedMessages);
+    d_maxUnconfirmedBytes    = bsl::move(rhs.d_maxUnconfirmedBytes);
+    d_consumerPriority       = bsl::move(rhs.d_consumerPriority);
+    d_expression             = bsl::move(rhs.d_expression);
+    return *this;
+}
+#endif
+
 inline Subscription& Subscription::setMaxUnconfirmedMessages(int value)
 {
     d_maxUnconfirmedMessages.emplace(value);