improve the code robustness of slist (#115)

slist.go

@@ -40,11 +40,17 @@ func (l *SList[T]) Clear() {
 
 // Front returns the first element in the list.
 func (l *SList[T]) Front() T {
+	if l.IsEmpty() {
+		panic("!IsEmpty")
+	}
 	return l.head.value
 }
 
 // Back returns the last element in the list.
 func (l *SList[T]) Back() T {
+	if l.IsEmpty() {
+		panic("!IsEmpty")
+	}
 	return l.tail.value
 }
 
@@ -74,14 +80,16 @@ func (l *SList[T]) PushBack(v T) {
 // PopFront popups an element from the front of the list.
 // The list must be non-empty!
 func (l *SList[T]) PopFront() T {
+	if l.IsEmpty() {
+		panic("!IsEmpty")
+	}
+
 	node := l.head
-	if node != nil {
-		l.head = node.next
-		if l.head == nil {
-			l.tail = nil
-		}
-		l.length--
+	l.head = node.next
+	if l.head == nil {
+		l.tail = nil
 	}
+	l.length--
 	return node.value
 }
 
@@ -166,19 +174,19 @@ type sListIterator[T any] struct {
 	node *sListNode[T]
 }
 
-func (it sListIterator[T]) IsNotEnd() bool {
+func (it *sListIterator[T]) IsNotEnd() bool {
 	return it.node != nil
 }
 
 func (it *sListIterator[T]) MoveToNext() {
 	it.node = it.node.next
 }
 
-func (it sListIterator[T]) Value() T {
+func (it *sListIterator[T]) Value() T {
 	return it.node.value
 }
 
-func (it sListIterator[T]) Pointer() *T {
+func (it *sListIterator[T]) Pointer() *T {
 	return &it.node.value
 }
 

slist_test.go

@@ -4,7 +4,7 @@ import (
 	"testing"
 )
 
-func Test_DList_Interface(t *testing.T) {
+func Test_SList_Interface(t *testing.T) {
 	sl := SList[int]{}
 	_ = Container(&sl)
 }
@@ -17,6 +17,44 @@ func Test_SList_Clean(t *testing.T) {
 	expectEq(t, sl.Len(), 0)
 }
 
+func Test_SList_Front(t *testing.T) {
+	t.Run("empty", func(t *testing.T) {
+		sl := SList[int]{}
+		expectPanic(t, func() { sl.Front() })
+	})
+
+	t.Run("normal", func(t *testing.T) {
+		sl := SList[int]{}
+		sl.PushFront(1)
+		expectEq(t, sl.Front(), 1)
+
+		sl.PushBack(2)
+		expectEq(t, sl.Front(), 1)
+
+		sl.PushFront(3)
+		expectEq(t, sl.Front(), 3)
+	})
+}
+
+func Test_SList_Back(t *testing.T) {
+	t.Run("empty", func(t *testing.T) {
+		sl := SList[int]{}
+		expectPanic(t, func() { sl.Back() })
+	})
+
+	t.Run("normal", func(t *testing.T) {
+		sl := SList[int]{}
+		sl.PushBack(1)
+		expectEq(t, sl.Back(), 1)
+
+		sl.PushFront(2)
+		expectEq(t, sl.Back(), 1)
+
+		sl.PushBack(3)
+		expectEq(t, sl.Back(), 3)
+	})
+}
+
 func Test_SList_PushFront(t *testing.T) {
 	sl := SList[int]{}
 	for i := 1; i < 10; i++ {
@@ -38,6 +76,8 @@ func Test_SList_PushBack(t *testing.T) {
 
 func Test_SList_PopFront(t *testing.T) {
 	sl := SList[int]{}
+	expectPanic(t, func() { sl.PopFront() })
+
 	sl.PushFront(1)
 	sl.PushFront(2)
 	expectEq(t, sl.PopFront(), 2)