datatypes: add a Queue.last() method (#12987)

vlib/datatypes/queue.v

@@ -15,11 +15,16 @@ pub fn (queue Queue<T>) len() int {
 	return queue.elements.len()
 }
 
-// peek returns the head of the queue
+// peek returns the head of the queue (first element added)
 pub fn (queue Queue<T>) peek() ?T {
 	return if !queue.is_empty() { queue.elements.first() ? } else { error('Queue is empty') }
 }
 
+// last returns the tail of the queue (last element added)
+pub fn (queue Queue<T>) last() ?T {
+	return if !queue.is_empty() { queue.elements.last() ? } else { error('Queue is empty') }
+}
+
 // push adds an element to the tail of the queue
 pub fn (mut queue Queue<T>) push(item T) {
 	queue.elements.push(item)

vlib/datatypes/queue_test.v

@@ -27,6 +27,17 @@ fn test_peek() ? {
 	assert false
 }
 
+fn test_last() ? {
+	mut queue := Queue<int>{}
+	queue.push(1)
+	assert queue.last() ? == 1
+	queue.push(2)
+	assert queue.last() ? == 2
+	queue = Queue<int>{}
+	queue.last() or { return }
+	assert false
+}
+
 fn test_push() ? {
 	mut queue := Queue<int>{}
 	queue.push(1)