[structs] change package structutil to structs (#81)

* refactor package structutil to structs

* add structs package zh-CN docs

structs/field.go

@@ -0,0 +1,112 @@
+package structs
+
+import (
+	"reflect"
+
+	"github.com/duke-git/lancet/v2/pointer"
+)
+
+// Field is abstract struct field for provide several high level functions
+type Field struct {
+	Struct
+	field reflect.StructField
+	tag   *Tag
+}
+
+func newField(v reflect.Value, f reflect.StructField, tagName string) *Field {
+	tag := f.Tag.Get(tagName)
+	field := &Field{
+		field: f,
+		tag:   newTag(tag),
+	}
+	field.rvalue = v
+	field.rtype = v.Type()
+	field.TagName = tagName
+	return field
+}
+
+// Tag returns the value that the key in the tag string.
+func (f *Field) Tag() *Tag {
+	return f.tag
+}
+
+// Value returns the underlying value of the field.
+func (f *Field) Value() any {
+	return f.rvalue.Interface()
+}
+
+// IsEmbedded returns true if the given field is an embedded field.
+func (f *Field) IsEmbedded() bool {
+	return len(f.field.Index) > 1
+}
+
+// IsExported returns true if the given field is exported.
+func (f *Field) IsExported() bool {
+	return f.field.IsExported()
+}
+
+// IsZero returns true if the given field is zero value.
+func (f *Field) IsZero() bool {
+	z := reflect.Zero(f.rvalue.Type()).Interface()
+	v := f.Value()
+	return reflect.DeepEqual(z, v)
+}
+
+// Name returns the name of the given field
+func (f *Field) Name() string {
+	return f.field.Name
+}
+
+// Kind returns the field's kind
+func (f *Field) Kind() reflect.Kind {
+	return f.rvalue.Kind()
+}
+
+// IsSlice check if a struct field type is slice or not
+func (f *Field) IsSlice() bool {
+	k := f.rvalue.Kind()
+	return k == reflect.Slice
+}
+
+// mapValue covert field value to map
+func (f *Field) mapValue(value any) any {
+	val := pointer.ExtractPointer(value)
+	v := reflect.ValueOf(val)
+	var ret any
+
+	switch v.Kind() {
+	case reflect.Struct:
+		s := New(val)
+		s.TagName = f.TagName
+		m, _ := s.ToMap()
+		ret = m
+	case reflect.Map:
+		mapEl := v.Type().Elem()
+		switch mapEl.Kind() {
+		case reflect.Ptr, reflect.Array, reflect.Map, reflect.Slice, reflect.Chan:
+			// iterate the map
+			m := make(map[string]any, v.Len())
+			for _, key := range v.MapKeys() {
+				m[key.String()] = f.mapValue(v.MapIndex(key).Interface())
+			}
+			ret = m
+		default:
+			ret = v.Interface()
+		}
+	case reflect.Slice, reflect.Array:
+		sEl := v.Type().Elem()
+		switch sEl.Kind() {
+		case reflect.Ptr, reflect.Array, reflect.Map, reflect.Slice, reflect.Chan:
+			slices := make([]any, v.Len())
+			for i := 0; i < v.Len(); i++ {
+				slices[i] = f.mapValue(v.Index(i).Interface())
+			}
+			ret = slices
+		default:
+			ret = v.Interface()
+		}
+	default:
+		ret = v.Interface()
+	}
+	return ret
+}