Return reference from emplace() in etl::queue (#992)

include/etl/queue.h

@@ -337,90 +337,107 @@ namespace etl
     //*************************************************************************
     /// Constructs a value in the queue 'in place'.
     /// If asserts or exceptions are enabled, throws an etl::queue_full if the queue if already full.
-    ///\param value The value to use to construct the item to push to the queue.
+    ///\param args The arguments to the constructor for the new item to push to the queue.
     //*************************************************************************
     template <typename ... Args>
-    void emplace(Args && ... args)
+    reference emplace(Args && ... args)
     {
 #if defined(ETL_CHECK_PUSH_POP)
       ETL_ASSERT(!full(), ETL_ERROR(queue_full));
 #endif
-      ::new (&p_buffer[in]) T(etl::forward<Args>(args)...);
+      reference value = p_buffer[in];
+      ::new (&value) T(etl::forward<Args>(args)...);
       add_in();
+      return value;
     }
 #else
     //*************************************************************************
-    /// Constructs a value in the queue 'in place'.
+    /// Constructs a default constructed value in the queue 'in place'.
     /// If asserts or exceptions are enabled, throws an etl::queue_full if the queue if already full.
-    ///\param value The value to use to construct the item to push to the queue.
     //*************************************************************************
-    void emplace()
+    reference emplace()
     {
 #if defined(ETL_CHECK_PUSH_POP)
       ETL_ASSERT(!full(), ETL_ERROR(queue_full));
 #endif
-      ::new (&p_buffer[in]) T();
+      reference value = p_buffer[in];
+      ::new (&value) T();
       add_in();
+      return value;
     }
 
     //*************************************************************************
     /// Constructs a value in the queue 'in place'.
     /// If asserts or exceptions are enabled, throws an etl::queue_full if the queue if already full.
-    ///\param value The value to use to construct the item to push to the queue.
+    ///\param value1 The argument to use to construct the item to push to the queue.
     //*************************************************************************
     template <typename T1>
-    void emplace(const T1& value1)
+    reference emplace(const T1& value1)
     {
 #if defined(ETL_CHECK_PUSH_POP)
       ETL_ASSERT(!full(), ETL_ERROR(queue_full));
 #endif
-      ::new (&p_buffer[in]) T(value1);
+      reference value = p_buffer[in];
+      ::new (&value) T(value1);
       add_in();
+      return value;
     }
 
     //*************************************************************************
     /// Constructs a value in the queue 'in place'.
     /// If asserts or exceptions are enabled, throws an etl::queue_full if the queue if already full.
-    ///\param value The value to use to construct the item to push to the queue.
+    ///\param value1 The first argument to use to construct the item to push to the queue.
+    ///\param value2 The second argument to use to construct the item to push to the queue.
     //*************************************************************************
     template <typename T1, typename T2>
-    void emplace(const T1& value1, const T2& value2)
+    reference emplace(const T1& value1, const T2& value2)
     {
 #if defined(ETL_CHECK_PUSH_POP)
       ETL_ASSERT(!full(), ETL_ERROR(queue_full));
 #endif
-      ::new (&p_buffer[in]) T(value1, value2);
+      reference value = p_buffer[in];
+      ::new (&value) T(value1, value2);
       add_in();
+      return value;
     }
 
     //*************************************************************************
     /// Constructs a value in the queue 'in place'.
     /// If asserts or exceptions are enabled, throws an etl::queue_full if the queue if already full.
-    ///\param value The value to use to construct the item to push to the queue.
+    ///\param value1 The first argument to use to construct the item to push to the queue.
+    ///\param value2 The second argument to use to construct the item to push to the queue.
+    ///\param value3 The third argument to use to construct the item to push to the queue.
     //*************************************************************************
     template <typename T1, typename T2, typename T3>
-    void emplace(const T1& value1, const T2& value2, const T3& value3)
+    reference emplace(const T1& value1, const T2& value2, const T3& value3)
     {
 #if defined(ETL_CHECK_PUSH_POP)
       ETL_ASSERT(!full(), ETL_ERROR(queue_full));
 #endif
-      ::new (&p_buffer[in]) T(value1, value2, value3);
+      reference value = p_buffer[in];
+      ::new (&value) T(value1, value2, value3);
       add_in();
+      return value;
     }
 
     //*************************************************************************
     /// Constructs a value in the queue 'in place'.
     /// If asserts or exceptions are enabled, throws an etl::queue_full if the queue if already full.
-    ///\param value The value to use to construct the item to push to the queue.
+    ///\param value1 The first argument to use to construct the item to push to the queue.
+    ///\param value2 The second argument to use to construct the item to push to the queue.
+    ///\param value3 The third argument to use to construct the item to push to the queue.
+    ///\param value4 The fourth argument to use to construct the item to push to the queue.
     //*************************************************************************
     template <typename T1, typename T2, typename T3, typename T4>
-    void emplace(const T1& value1, const T2& value2, const T3& value3, const T4& value4)
+    reference emplace(const T1& value1, const T2& value2, const T3& value3, const T4& value4)
     {
 #if defined(ETL_CHECK_PUSH_POP)
       ETL_ASSERT(!full(), ETL_ERROR(queue_full));
 #endif
-      ::new (&p_buffer[in]) T(value1, value2, value3, value4);
+      reference value = p_buffer[in];
+      ::new (&value) T(value1, value2, value3, value4);
       add_in();
+      return value;
     }
 #endif
 

test/test_queue.cpp

@@ -369,11 +369,17 @@ namespace
     {
       etl::queue<Item, 5> queue;
 
-      queue.emplace();
-      queue.emplace('b', 2, 2.3); 
-      queue.emplace('c', 3, 3.4);
-      queue.emplace('d', 4, 4.5);
-      queue.emplace('e', 5, 5.6);
+      Item& item_a = queue.emplace();
+      Item& item_b = queue.emplace('b', 2, 2.3);
+      Item& item_c = queue.emplace('c', 3, 3.4);
+      Item& item_d = queue.emplace('d', 4, 4.5);
+      Item& item_e = queue.emplace('e', 5, 5.6);
+
+      CHECK(item_a == Item('a', 1, 1.2));
+      CHECK(item_b == Item('b', 2, 2.3));
+      CHECK(item_c == Item('c', 3, 3.4));
+      CHECK(item_d == Item('d', 4, 4.5));
+      CHECK(item_e == Item('e', 5, 5.6));
 
       CHECK(queue.front() == Item('a', 1, 1.2));
       queue.pop();