Use generics for Add and Delete Methods

entry.go

@@ -68,120 +68,80 @@ func NewEntry(title string) *Entry {
 
 // AddAuthor adds the Person as an author to the Entry.
 func (e *Entry) AddAuthor(p *Person) {
-	if e.Authors == nil {
-		e.Authors = make([]*Person, 1)
-		e.Authors[0] = p
-	} else {
-		e.Authors = append(e.Authors, p)
-	}
-
+	addToSlice(e.Authors, p)
 	e.Updated = NewDate(time.Now())
 }
 
 // DeleteAuthor deletes the Person from the Entry. It return an error.
 func (e *Entry) DeleteAuthor(id int) error {
-	length := len(e.Authors)
-	if id > length {
-		return fmt.Errorf("error deleting author from entry %v: id %v out of range %v", e.ID.URI, id, length)
+	if err := deleteFromSlice(e.Authors, id); err != nil {
+		return fmt.Errorf("error deleting author %v from entry %v: %v", id, e.ID.URI, err)
 	}
 
-	e.Authors = append(e.Authors[:id], e.Authors[id+1:]...)
 	e.Updated = NewDate(time.Now())
 	return nil
 }
 
 // AddCategory adds the Category to the Entry.
 func (e *Entry) AddCategory(c *Category) {
-	if e.Categories == nil {
-		e.Categories = make([]*Category, 1)
-		e.Categories[0] = c
-	} else {
-		e.Categories = append(e.Categories, c)
-	}
-
+	addToSlice(e.Categories, c)
 	e.Updated = NewDate(time.Now())
 }
 
 // DeleteCategory deletes the Category from the Entry. It return an error.
 func (e *Entry) DeleteCategory(id int) error {
-	length := len(e.Categories)
-	if id > length {
-		return fmt.Errorf("error deleting category from entry %v: id %v out of range %v", e.ID.URI, id, length)
+	if err := deleteFromSlice(e.Categories, id); err != nil {
+		return fmt.Errorf("error deleting category %v from entry %v: %v", id, e.ID.URI, err)
 	}
 
-	e.Categories = append(e.Categories[:id], e.Categories[id+1:]...)
 	e.Updated = NewDate(time.Now())
 	return nil
 }
 
 // AddContributor adds the Person as a contributor to the Entry.
 func (e *Entry) AddContributor(c *Person) {
-	if e.Contributors == nil {
-		e.Contributors = make([]*Person, 1)
-		e.Contributors[0] = c
-	} else {
-		e.Contributors = append(e.Contributors, c)
-	}
-
+	addToSlice(e.Contributors, c)
 	e.Updated = NewDate(time.Now())
 }
 
 // DeleteContributor deletes the Person from the Entry. It return an error.
 func (e *Entry) DeleteContributor(id int) error {
-	length := len(e.Contributors)
-	if id > length {
-		return fmt.Errorf("error deleting contributor from entry %v: id %v out of range %v", e.ID.URI, id, length)
+	if err := deleteFromSlice(e.Contributors, id); err != nil {
+		return fmt.Errorf("error deleting contributor %v from entry %v: %v", id, e.ID.URI, err)
 	}
 
-	e.Contributors = append(e.Contributors[:id], e.Contributors[id+1:]...)
 	e.Updated = NewDate(time.Now())
 	return nil
 }
 
 // AddLink adds the Link to the Entry.
 func (e *Entry) AddLink(l *Link) {
-	if e.Links == nil {
-		e.Links = make([]*Link, 1)
-		e.Links[0] = l
-	} else {
-		e.Links = append(e.Links, l)
-	}
-
+	addToSlice(e.Links, l)
 	e.Updated = NewDate(time.Now())
 }
 
 // DeleteLink deletes the Link from the Entry. It return an error.
 func (e *Entry) DeleteLink(id int) error {
-	length := len(e.Links)
-	if id > length {
-		return fmt.Errorf("error deleting link from entry %v: id %v out of range %v", e.ID.URI, id, length)
+	if err := deleteFromSlice(e.Links, id); err != nil {
+		return fmt.Errorf("error deleting link %v from entry %v: %v", id, e.ID.URI, err)
 	}
 
-	e.Links = append(e.Links[:id], e.Links[id+1:]...)
 	e.Updated = NewDate(time.Now())
 	return nil
 }
 
 // AddExtension adds the ExtensionElement to the Entry.
 func (e *Entry) AddExtension(x *ExtensionElement) {
-	if e.Extensions == nil {
-		e.Extensions = make([]*ExtensionElement, 1)
-		e.Extensions[0] = x
-	} else {
-		e.Extensions = append(e.Extensions, x)
-	}
-
+	addToSlice(e.Extensions, x)
 	e.Updated = NewDate(time.Now())
 }
 
 // DeleteExtension deletes the Extension from the Entry. It return an error.
 func (e *Entry) DeleteExtension(id int) error {
-	length := len(e.Extensions)
-	if id > length {
-		return fmt.Errorf("error deleting extension from entry %v: id %v out of range %v", e.ID.URI, id, length)
+	if err := deleteFromSlice(e.Extensions, id); err != nil {
+		return fmt.Errorf("error deleting extension %v from entry %v: %v", id, e.ID.URI, err)
 	}
 
-	e.Extensions = append(e.Extensions[:id], e.Extensions[id+1:]...)
 	e.Updated = NewDate(time.Now())
 	return nil
 }