datatypes: add an index method on LinkedList and Queue (#13185)

vlib/datatypes/linked_list.v

@@ -40,6 +40,25 @@ pub fn (list LinkedList<T>) last() ?T {
 	}
 }
 
+// index returns the element at the given index of the linked list
+pub fn (list LinkedList<T>) index(idx int) ?T {
+	if list.head == 0 {
+		return error('Linked list is empty')
+	} else {
+		mut node := list.head
+		mut iterations := 0
+		for node.next != 0 && iterations < idx {
+			node = node.next
+			iterations++
+		}
+		if iterations == idx {
+			return node.data
+		} else {
+			return error('Index out of bounds')
+		}
+	}
+}
+
 // push adds an element to the end of the linked list
 pub fn (mut list LinkedList<T>) push(item T) {
 	new_node := &ListNode{

vlib/datatypes/linked_list_test.v

@@ -38,6 +38,17 @@ fn test_last() ? {
 	assert false
 }
 
+fn test_index() ? {
+	mut list := LinkedList<int>{}
+	list.push(1)
+	assert list.index(0) ? == 1
+	list.push(2)
+	assert list.index(1) ? == 2
+	list.pop() ?
+	list.index(1) or { return }
+	assert false
+}
+
 fn test_push() ? {
 	mut list := LinkedList<int>{}
 	list.push(1)

vlib/datatypes/queue.v

@@ -17,12 +17,17 @@ pub fn (queue Queue<T>) len() int {
 
 // 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') }
+	return queue.elements.first()
 }
 
 // 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') }
+	return queue.elements.last()
+}
+
+// index returns the element at the given index of the queue
+pub fn (queue Queue<T>) index(idx int) ?T {
+	return queue.elements.index(idx)
 }
 
 // push adds an element to the tail of the queue
@@ -32,7 +37,7 @@ pub fn (mut queue Queue<T>) push(item T) {
 
 // pop removes the element at the head of the queue and returns it
 pub fn (mut queue Queue<T>) pop() ?T {
-	return if !queue.is_empty() { queue.elements.shift() ? } else { error('Queue is empty') }
+	return queue.elements.shift()
 }
 
 // str returns a string representation of the queue

vlib/datatypes/queue_test.v

@@ -38,6 +38,17 @@ fn test_last() ? {
 	assert false
 }
 
+fn test_index() ? {
+	mut queue := Queue<int>{}
+	queue.push(1)
+	assert queue.index(0) ? == 1
+	queue.push(2)
+	assert queue.index(1) ? == 2
+	queue.pop() ?
+	queue.index(1) or { return }
+	assert false
+}
+
 fn test_push() ? {
 	mut queue := Queue<int>{}
 	queue.push(1)