remove Element interface as it complicates nil checks

element.go

@@ -3,36 +3,29 @@ package jsonmap
 type Key = string
 type Value = any
 
-type Element interface {
-	Key() Key
-	Value() Value
-	Next() Element
-	Prev() Element
-}
-
-// element is an element of a map, to be used in iteration.
+// Element of a map, to be used in iteration.
 //
 //	for elem := m.First(); elem != nil; elem = elem.Next() {
 //	    fmt.Println(elem.Key(), elem.Value())
 //	}
-type element struct {
+type Element struct {
 	key   Key
 	value Value
 
-	next, prev *element
+	next, prev *Element
 }
 
 // Key returns the key of the element.
 //
 //	key := elem.Key()
-func (e *element) Key() Key {
+func (e *Element) Key() Key {
 	return e.key
 }
 
 // Value returns the value of the element.
 //
 //	value := elem.Value()
-func (e *element) Value() Value {
+func (e *Element) Value() Value {
 	return e.value
 }
 
@@ -43,7 +36,7 @@ func (e *element) Value() Value {
 //	for elem := m.First(); elem != nil; elem = elem.Next() {
 //	    fmt.Println(elem.Key(), elem.Value())
 //	}
-func (e *element) Next() Element {
+func (e *Element) Next() *Element {
 	return e.next
 }
 
@@ -54,6 +47,6 @@ func (e *element) Next() Element {
 //	for elem := m.Last(); elem != nil; elem = elem.Prev() {
 //	    fmt.Println(elem.Key(), elem.Value())
 //	}
-func (e *element) Prev() Element {
+func (e *Element) Prev() *Element {
 	return e.prev
 }

extra.go

@@ -9,7 +9,7 @@ func (m *Map) SetFront(key Key, value Value) {
 		elem.value = value
 		return
 	}
-	elem := &element{
+	elem := &Element{
 		key:   key,
 		value: value,
 	}

jsonmap.go

@@ -7,24 +7,24 @@ package jsonmap
 // serializing to JSON, and has additional methods to iterate from any element.
 // Similar to native map, user has to take care of concurrent access and nil map value.
 type Map struct {
-	elements    map[Key]*element
-	first, last *element
+	elements    map[Key]*Element
+	first, last *Element
 }
 
 // New returns a new map. O(1) time.
 //
 //	m := jsonmap.New()
 func New() *Map {
 	return &Map{
-		elements: make(map[Key]*element),
+		elements: make(map[Key]*Element),
 	}
 }
 
 // Clear removes all elements from the map. O(1) time.
 //
 //	m.Clear()
 func (m *Map) Clear() {
-	m.elements = make(map[Key]*element)
+	m.elements = make(map[Key]*Element)
 	m.first = nil
 	m.last = nil
 }
@@ -72,7 +72,7 @@ func (m *Map) Set(key Key, value Value) {
 		elem.value = value
 		return
 	}
-	elem := &element{
+	elem := &Element{
 		key:   key,
 		value: value,
 	}
@@ -136,20 +136,23 @@ func (m *Map) Pop() (key Key, value Value, ok bool) {
 // First returns the first element in the map, for iteration.
 // Returns nil if the map is empty.
 // O(1) time.
-func (m *Map) First() Element {
+func (m *Map) First() *Element {
 	return m.first
 }
 
 // Last returns the last element in the map, for iteration for backwards iteration.
 // Returns nil if the map is empty.
 // O(1) time.
-func (m *Map) Last() Element {
+func (m *Map) Last() *Element {
 	return m.last
 }
 
 // GetElement returns the element for the key, for iteration from a needle.
 // Returns nil if the key is not in the map.
 // O(1) time.
-func (m *Map) GetElement(key Key) Element {
-	return m.elements[key]
+func (m *Map) GetElement(key Key) *Element {
+	if el, ok := m.elements[key]; ok {
+		return el
+	}
+	return nil
 }

simplemap/element.go

@@ -1,28 +1,26 @@
 package jsonmap
 
-import "github.com/metalim/jsonmap"
-
-// element is an element of a map, to be used in iteration.
+// Element of a map, to be used in iteration.
 //
 //	for elem := m.First(); elem != nil; elem = elem.Next() {
 //	    fmt.Println(elem.Key(), elem.Value())
 //	}
-type element struct {
+type Element struct {
 	m     *Map
 	index int
 }
 
 // Key returns the key of the element.
 //
 //	key := elem.Key()
-func (e *element) Key() Key {
+func (e *Element) Key() Key {
 	return e.m.keys[e.index]
 }
 
 // Value returns the value of the element.
 //
 //	value := elem.Value()
-func (e *element) Value() Value {
+func (e *Element) Value() Value {
 	return e.m.values[e.Key()]
 }
 
@@ -33,11 +31,11 @@ func (e *element) Value() Value {
 //	for elem := m.First(); elem != nil; elem = elem.Next() {
 //	    fmt.Println(elem.Key(), elem.Value())
 //	}
-func (e *element) Next() jsonmap.Element {
+func (e *Element) Next() *Element {
 	if e.index == len(e.m.keys)-1 {
 		return nil
 	}
-	return &element{
+	return &Element{
 		m:     e.m,
 		index: e.index + 1,
 	}
@@ -50,11 +48,11 @@ func (e *element) Next() jsonmap.Element {
 //	for elem := m.Last(); elem != nil; elem = elem.Prev() {
 //	    fmt.Println(elem.Key(), elem.Value())
 //	}
-func (e *element) Prev() jsonmap.Element {
+func (e *Element) Prev() *Element {
 	if e.index == 0 {
 		return nil
 	}
-	return &element{
+	return &Element{
 		m:     e.m,
 		index: e.index - 1,
 	}
@@ -67,8 +65,8 @@ func (e *element) Prev() jsonmap.Element {
 //	for elem := m.First(); elem != nil; elem = elem.Next() {
 //	    fmt.Println(elem.Key(), elem.Value())
 //	}
-func (m *Map) First() jsonmap.Element {
-	return &element{
+func (m *Map) First() *Element {
+	return &Element{
 		m:     m,
 		index: 0,
 	}
@@ -81,8 +79,8 @@ func (m *Map) First() jsonmap.Element {
 //	for elem := m.Last(); elem != nil; elem = elem.Prev() {
 //	    fmt.Println(elem.Key(), elem.Value())
 //	}
-func (m *Map) Last() jsonmap.Element {
-	return &element{
+func (m *Map) Last() *Element {
+	return &Element{
 		m:     m,
 		index: len(m.keys) - 1,
 	}
@@ -91,11 +89,11 @@ func (m *Map) Last() jsonmap.Element {
 // GetElement returns the element for the key, for iteration from a needle.
 // Returns nil if the key is not in the map.
 // O(n) for existing keys, because it uses KeyIndex().
-func (m *Map) GetElement(key Key) jsonmap.Element {
+func (m *Map) GetElement(key Key) *Element {
 	if _, ok := m.values[key]; !ok {
 		return nil
 	}
-	return &element{
+	return &Element{
 		m:     m,
 		index: m.KeyIndex(key),
 	}

slow.go

@@ -52,7 +52,7 @@ func (m *Map) SortKeys(less func(a, b Key) bool) {
 	if m.Len() < 2 {
 		return
 	}
-	elements := make([]*element, 0, len(m.elements))
+	elements := make([]*Element, 0, len(m.elements))
 	for elem := m.first; elem != nil; elem = elem.next {
 		elements = append(elements, elem)
 	}

test/interface_test.go

@@ -27,11 +27,19 @@ type IMap interface {
 	String() string
 	Keys() []Key
 	Values() []Value
-
-	First() jsonmap.Element
-	Last() jsonmap.Element
-	GetElement(key Key) jsonmap.Element
+}
+type IJSONMap interface {
+	First() *jsonmap.Element
+	Last() *jsonmap.Element
+	GetElement(key Key) *jsonmap.Element
+}
+type ISimpleMap interface {
+	First() *simplemap.Element
+	Last() *simplemap.Element
+	GetElement(key Key) *simplemap.Element
 }
 
 var _ IMap = (*jsonmap.Map)(nil)
 var _ IMap = (*simplemap.Map)(nil)
+var _ IJSONMap = (*jsonmap.Map)(nil)
+var _ ISimpleMap = (*simplemap.Map)(nil)

test/jsonmap_test.go

@@ -18,8 +18,38 @@ func TestJSONMap(t *testing.T) {
 
 func testJSONMapOnce(t *testing.T, i int) {
 	m := jsonmap.New()
+	// no elements
+	assert.Equal(t, m.Len(), 0)
+	assert.Equal(t, len(m.Keys()), 0)
+	assert.Equal(t, m.String(), "map[]")
+	assert.Nil(t, m.First())
+	assert.Nil(t, m.Last())
+
+	// 1 element
 	m.Set("a", 1)
+	assert.Equal(t, m.Len(), 1)
+	assert.Equal(t, len(m.Keys()), 1)
+	assert.Equal(t, m.Keys()[0], "a")
+	assert.Equal(t, m.First().Key(), m.Keys()[0])
+	assert.Equal(t, m.First().Key(), m.Last().Key())
+	assert.Nil(t, m.First().Next())
+	assert.Nil(t, m.Last().Prev())
+	assert.Equal(t, m.String(), "map[a:1]")
+
+	// 2 elements
 	m.Set("d", "2")
+	assert.Equal(t, m.Len(), 2)
+	assert.Equal(t, len(m.Keys()), 2)
+	assert.Equal(t, m.Keys()[0], "a")
+	assert.Equal(t, m.Keys()[1], "d")
+	assert.Equal(t, m.First().Key(), m.Keys()[0])
+	assert.Equal(t, m.Last().Key(), m.Keys()[1])
+	assert.Nil(t, m.First().Prev())
+	assert.Equal(t, m.First().Next(), m.Last())
+	assert.Equal(t, m.Last().Prev(), m.First())
+	assert.Nil(t, m.Last().Next())
+	assert.Equal(t, m.String(), "map[a:1 d:2]")
+
 	m.Set("c", 3)
 	m.Set("e", 5)
 	m.Set("b", 6)
@@ -61,8 +91,8 @@ func testJSONMapOnce(t *testing.T, i int) {
 	assert.Equal(t, v.(int), 7)
 	v, ok = m.Get("c")
 	assert.True(t, !ok)
-	assert.Equal(t, v, nil)
+	assert.Nil(t, v)
 	v, ok = m.Get("e")
 	assert.True(t, !ok)
-	assert.Equal(t, v, nil)
+	assert.Nil(t, v)
 }