Return the index of the added element

README.md

@@ -2,7 +2,7 @@
 
 An extensible Atom feed generator library that aims to be very close to RFC4287.
 It diligently checks for compliance with the standard and provides functions for
-easy creation and extension of elements.
+easy creation, extension and deletion of elements.
 
 ## Installation
 
@@ -14,9 +14,9 @@ go get git.streifling.com/jason/atom@latest
 
 ## Usage
 
-This library provides convenient functions to safely create and extend elements
-and attributes of Atom feeds. It also provides checks for all constructs'
-adherence to RFC4287.
+This library provides convenient functions to safely create, extend and delete
+elements and attributes of Atom feeds. It also provides checks for all
+constructs' adherence to RFC4287.
 
 ```go
 package main
@@ -30,8 +30,6 @@ import (
 
 func main() {
  feed := atom.NewFeed("Example Feed")
- feed.Title = atom.NewText("text", "Example Feed")
- feed.ID = atom.NewID(atom.NewURN())
  if err := feed.Check(); err != nil {
   log.Fatalln(err)
  }
@@ -44,7 +42,6 @@ func main() {
  feed.AddAuthor(author)
 
  entry := atom.NewEntry("First Entry")
- entry.ID = atom.NewID(atom.NewURN())
  entry.Content = atom.NewContent(atom.InlineText, "text", "This is the content of the first entry.")
  if err := entry.Check(); err != nil {
   log.Fatalln(err)

atom.go

@@ -1,6 +1,7 @@
 package atom
 
 import (
+	"encoding/xml"
 	"fmt"
 	"html"
 	"mime"
@@ -11,6 +12,32 @@ import (
 	"golang.org/x/text/language"
 )
 
+type Countable interface {
+	*xml.Attr | *Person | *Category | *Link | *ExtensionElement | *Entry
+}
+
+// addToSlice adds a Countable to to a *[]Countable. It returns an int.
+func addToSlice[C Countable](slice *[]C, countable C) int {
+	if *slice == nil {
+		*slice = make([]C, 0)
+	}
+	*slice = append(*slice, countable)
+
+	return len(*slice) - 1
+}
+
+// deleteFromSlice deletes the Countable with the index from the *[]Countable.
+// It return an error.
+func deleteFromSlice[C Countable](slice *[]C, index int) error {
+	length := len(*slice)
+	if index > length {
+		return fmt.Errorf("id %v out of range %v", index, length)
+	}
+
+	*slice = append((*slice)[:index], (*slice)[index+1:]...)
+	return nil
+}
+
 // isValidIRI checks whether an IRI is valid or not. It returns a bool.
 // https://www.w3.org/2011/04/XMLSchema/TypeLibrary-IRI-RFC3987.xsd
 func isValidIRI(iri string) bool {

commonAttributes.go

@@ -17,25 +17,17 @@ func newCommonAttributes() *CommonAttributes {
 	return new(CommonAttributes)
 }
 
-// AddAttribute adds the attribute to the CommonAttributes.
-func (c *CommonAttributes) AddAttribute(name, value string) {
-	if c.UndefinedAttributes == nil {
-		c.UndefinedAttributes = make([]*xml.Attr, 1)
-		c.UndefinedAttributes[0] = &xml.Attr{Name: xml.Name{Local: name}, Value: value}
-	} else {
-		c.UndefinedAttributes = append(c.UndefinedAttributes, &xml.Attr{Name: xml.Name{Local: name}, Value: value})
-	}
+// AddAttribute adds the attribute to the CommonAttributes. It returns an int.
+func (c *CommonAttributes) AddAttribute(name, value string) int {
+	return addToSlice(&c.UndefinedAttributes, &xml.Attr{Name: xml.Name{Local: name}, Value: value})
 }
 
-// DeleteAttribute deletes the attribute from the CommonAttributes. It return an
-// error.
-func (c *CommonAttributes) DeleteAttribute(id int) error {
-	length := len(c.UndefinedAttributes)
-	if id > length {
-		return fmt.Errorf("error deleting undefined attribute from common attributes %v: id %v out of range %v", c, id, length)
+// DeleteAttribute deletes the attribute at index from the CommonAttributes. It
+// return an error.
+func (c *CommonAttributes) DeleteAttribute(index int) error {
+	if err := deleteFromSlice(&c.UndefinedAttributes, index); err != nil {
+		return fmt.Errorf("error deleting undefined attribute %v from common attributes %v: %v", index, c, err)
 	}
-
-	c.UndefinedAttributes = append(c.UndefinedAttributes[:id], c.UndefinedAttributes[id+1:]...)
 	return nil
 }
 

entry.go

@@ -66,122 +66,86 @@ 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)
-	}
-
+// AddAuthor adds the Person as an author to the Entry. It returns an int.
+func (e *Entry) AddAuthor(p *Person) int {
 	e.Updated = NewDate(time.Now())
+	return addToSlice(&e.Authors, p)
 }
 
-// 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)
+// DeleteAuthor deletes the Person at index from the Entry. It return an error.
+func (e *Entry) DeleteAuthor(index int) error {
+	if err := deleteFromSlice(&e.Authors, index); err != nil {
+		return fmt.Errorf("error deleting author %v from entry %v: %v", index, 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)
-	}
-
+// AddCategory adds the Category to the Entry. It returns an int.
+func (e *Entry) AddCategory(c *Category) int {
 	e.Updated = NewDate(time.Now())
+	return addToSlice(&e.Categories, c)
 }
 
-// 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)
+// DeleteCategory deletes the Category at index from the Entry. It return an
+// error.
+func (e *Entry) DeleteCategory(index int) error {
+	if err := deleteFromSlice(&e.Categories, index); err != nil {
+		return fmt.Errorf("error deleting category %v from entry %v: %v", index, 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)
-	}
-
+// AddContributor adds the Person as a contributor to the Entry. It returns an
+// int.
+func (e *Entry) AddContributor(c *Person) int {
 	e.Updated = NewDate(time.Now())
+	return addToSlice(&e.Contributors, c)
 }
 
-// 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)
+// DeleteContributor deletes the Person at index from the Entry. It return an
+// error.
+func (e *Entry) DeleteContributor(index int) error {
+	if err := deleteFromSlice(&e.Contributors, index); err != nil {
+		return fmt.Errorf("error deleting contributor %v from entry %v: %v", index, 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)
-	}
-
+// AddLink adds the Link to the Entry. It returns an int.
+func (e *Entry) AddLink(l *Link) int {
 	e.Updated = NewDate(time.Now())
+	return addToSlice(&e.Links, l)
 }
 
-// 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)
+// DeleteLink deletes the Link at index from the Entry. It return an error.
+func (e *Entry) DeleteLink(index int) error {
+	if err := deleteFromSlice(&e.Links, index); err != nil {
+		return fmt.Errorf("error deleting link %v from entry %v: %v", index, 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)
-	}
-
+// AddExtension adds the ExtensionElement to the Entry. It returns an int.
+func (e *Entry) AddExtension(x *ExtensionElement) int {
 	e.Updated = NewDate(time.Now())
+	return addToSlice(&e.Extensions, x)
 }
 
-// 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)
+// DeleteExtension deletes the Extension at index from the Entry. It return an
+// error.
+func (e *Entry) DeleteExtension(index int) error {
+	if err := deleteFromSlice(&e.Extensions, index); err != nil {
+		return fmt.Errorf("error deleting extension %v from entry %v: %v", index, e.ID.URI, err)
 	}
 
-	e.Extensions = append(e.Extensions[:id], e.Extensions[id+1:]...)
 	e.Updated = NewDate(time.Now())
 	return nil
 }

feed.go

@@ -35,146 +35,103 @@ func NewFeed(title string) *Feed {
 	}
 }
 
-// AddAuthor adds the Person as an author to the Feed.
-func (f *Feed) AddAuthor(p *Person) {
-	if f.Authors == nil {
-		f.Authors = make([]*Person, 1)
-		f.Authors[0] = p
-	} else {
-		f.Authors = append(f.Authors, p)
-	}
-
+// AddAuthor adds the Person as an author to the Feed. It returns an int.
+func (f *Feed) AddAuthor(p *Person) int {
 	f.Updated = NewDate(time.Now())
+	return addToSlice(&f.Authors, p)
 }
 
-// DeleteAuthor deletes the Person from the Feed. It return an error.
-func (f *Feed) DeleteAuthor(id int) error {
-	length := len(f.Authors)
-	if id > length {
-		return fmt.Errorf("error deleting author from feed %v: id %v out of range %v", f.ID.URI, id, length)
+// DeleteAuthor deletes the Person at index from the Feed. It return an error.
+func (f *Feed) DeleteAuthor(index int) error {
+	if err := deleteFromSlice(&f.Authors, index); err != nil {
+		return fmt.Errorf("error deleting author %v from entry %v: %v", index, f.ID.URI, err)
 	}
 
-	f.Authors = append(f.Authors[:id], f.Authors[id+1:]...)
 	f.Updated = NewDate(time.Now())
 	return nil
 }
 
-// AddCategory adds the Category to the Feed.
-func (f *Feed) AddCategory(c *Category) {
-	if f.Categories == nil {
-		f.Categories = make([]*Category, 1)
-		f.Categories[0] = c
-	} else {
-		f.Categories = append(f.Categories, c)
-	}
-
+// AddCategory adds the Category to the Feed. It returns an int.
+func (f *Feed) AddCategory(c *Category) int {
 	f.Updated = NewDate(time.Now())
+	return addToSlice(&f.Categories, c)
 }
 
-// DeleteCategory deletes the Category from the Feed. It return an error.
-func (f *Feed) DeleteCategory(id int) error {
-	length := len(f.Categories)
-	if id > length {
-		return fmt.Errorf("error deleting category from feed %v: id %v out of range %v", f.ID.URI, id, length)
+// DeleteCategory deletes the Category at index from the Feed. It return an
+// error.
+func (f *Feed) DeleteCategory(index int) error {
+	if err := deleteFromSlice(&f.Categories, index); err != nil {
+		return fmt.Errorf("error deleting category %v from entry %v: %v", index, f.ID.URI, err)
 	}
 
-	f.Categories = append(f.Categories[:id], f.Categories[id+1:]...)
 	f.Updated = NewDate(time.Now())
 	return nil
 }
 
-// AddContributor adds the Person as a contributor to the Feed.
-func (f *Feed) AddContributor(c *Person) {
-	if f.Contributors == nil {
-		f.Contributors = make([]*Person, 1)
-		f.Contributors[0] = c
-	} else {
-		f.Contributors = append(f.Contributors, c)
-	}
-
+// AddContributor adds the Person as a contributor to the Feed. It returns an
+// int.
+func (f *Feed) AddContributor(c *Person) int {
 	f.Updated = NewDate(time.Now())
+	return addToSlice(&f.Contributors, c)
 }
 
-// DeleteContributor deletes the Person from the Feed. It return an error.
-func (f *Feed) DeleteContributor(id int) error {
-	length := len(f.Contributors)
-	if id > length {
-		return fmt.Errorf("error deleting contributor from feed %v: id %v out of range %v", f.ID.URI, id, length)
+// DeleteContributor deletes the Person at index from the Feed. It return an
+// error.
+func (f *Feed) DeleteContributor(index int) error {
+	if err := deleteFromSlice(&f.Contributors, index); err != nil {
+		return fmt.Errorf("error deleting contributor %v from entry %v: %v", index, f.ID.URI, err)
 	}
 
-	f.Contributors = append(f.Contributors[:id], f.Contributors[id+1:]...)
 	f.Updated = NewDate(time.Now())
 	return nil
 }
 
 // AddLink adds the Link to the Feed. There should be one Link with Rel "self".
-func (f *Feed) AddLink(l *Link) {
-	if f.Links == nil {
-		f.Links = make([]*Link, 1)
-		f.Links[0] = l
-	} else {
-		f.Links = append(f.Links, l)
-	}
-
+// It returns an int.
+func (f *Feed) AddLink(l *Link) int {
 	f.Updated = NewDate(time.Now())
+	return addToSlice(&f.Links, l)
 }
 
-// DeleteLink deletes the Link from the Feed. It return an error.
-func (f *Feed) DeleteLink(id int) error {
-	length := len(f.Links)
-	if id > length {
-		return fmt.Errorf("error deleting link from feed %v: id %v out of range %v", f.ID.URI, id, length)
+// DeleteLink deletes the Link at index from the Feed. It return an error.
+func (f *Feed) DeleteLink(index int) error {
+	if err := deleteFromSlice(&f.Links, index); err != nil {
+		return fmt.Errorf("error deleting link %v from entry %v: %v", index, f.ID.URI, err)
 	}
 
-	f.Links = append(f.Links[:id], f.Links[id+1:]...)
 	f.Updated = NewDate(time.Now())
 	return nil
 }
 
-// AddExtension adds the Extension to the Feed.
-func (f *Feed) AddExtension(e *ExtensionElement) {
-	if f.Extensions == nil {
-		f.Extensions = make([]*ExtensionElement, 1)
-		f.Extensions[0] = e
-	} else {
-		f.Extensions = append(f.Extensions, e)
-	}
-
+// AddExtension adds the Extension to the Feed. It returns an int.
+func (f *Feed) AddExtension(e *ExtensionElement) int {
 	f.Updated = NewDate(time.Now())
+	return addToSlice(&f.Extensions, e)
 }
 
-// DeleteExtension deletes the Extension from the Feed. It return an error.
-func (f *Feed) DeleteExtension(id int) error {
-	length := len(f.Extensions)
-	if id > length {
-		return fmt.Errorf("error deleting extension from feed %v: id %v out of range %v", f.ID.URI, id, length)
+// DeleteExtension deletes the Extension at index from the Feed. It return an
+// error.
+func (f *Feed) DeleteExtension(index int) error {
+	if err := deleteFromSlice(&f.Extensions, index); err != nil {
+		return fmt.Errorf("error deleting extension %v from entry %v: %v", index, f.ID.URI, err)
 	}
 
-	f.Extensions = append(f.Extensions[:id], f.Extensions[id+1:]...)
 	f.Updated = NewDate(time.Now())
 	return nil
 }
 
-// AddEntry adds the Entry to the Feed.
-func (f *Feed) AddEntry(e *Entry) {
-	if f.Entries == nil {
-		f.Entries = make([]*Entry, 1)
-		f.Entries[0] = e
-	} else {
-		f.Entries = append(f.Entries, e)
-	}
-
+// AddEntry adds the Entry to the Feed. It returns an int.
+func (f *Feed) AddEntry(e *Entry) int {
 	f.Updated = NewDate(time.Now())
+	return addToSlice(&f.Entries, e)
 }
 
-// DeleteEntry deletes the Entry from the Feed. It return an error.
-func (f *Feed) DeleteEntry(id int) error {
-	length := len(f.Entries)
-	if id > length {
-		return fmt.Errorf("error deleting entry from feed %v: id %v out of range %v", f.ID.URI, id, length)
+// DeleteEntry deletes the Entry at index from the Feed. It return an error.
+func (f *Feed) DeleteEntry(index int) error {
+	if err := deleteFromSlice(&f.Entries, index); err != nil {
+		return fmt.Errorf("error deleting entry %v from entry %v: %v", index, f.ID.URI, err)
 	}
 
-	f.Entries = append(f.Entries[:id], f.Entries[id+1:]...)
 	f.Updated = NewDate(time.Now())
 	return nil
 }

person.go

@@ -21,24 +21,17 @@ func NewPerson(name string) *Person {
 	}
 }
 
-// AddExtension adds the Extension to the Person.
-func (p *Person) AddExtension(e *ExtensionElement) {
-	if p.Extensions == nil {
-		p.Extensions = make([]*ExtensionElement, 1)
-		p.Extensions[0] = e
-	} else {
-		p.Extensions = append(p.Extensions, e)
-	}
+// AddExtension adds the Extension to the Person. It returns an int.
+func (p *Person) AddExtension(e *ExtensionElement) int {
+	return addToSlice(&p.Extensions, e)
 }
 
-// DeleteExtension deletes the Extension from the Person. It return an error.
-func (p *Person) DeleteExtension(id int) error {
-	length := len(p.Extensions)
-	if id > length {
-		return fmt.Errorf("error deleting extension from person %v: id %v out of range %v", p, id, length)
+// DeleteExtension deletes the Extension at index from the Person. It return an
+// error.
+func (p *Person) DeleteExtension(index int) error {
+	if err := deleteFromSlice(&p.Extensions, index); err != nil {
+		return fmt.Errorf("error deleting extension %v from person %v: %v", index, p, err)
 	}
-
-	p.Extensions = append(p.Extensions[:id], p.Extensions[id+1:]...)
 	return nil
 }
 

source.go

@@ -28,108 +28,72 @@ func NewSource() *Source {
 	return &Source{CommonAttributes: newCommonAttributes()}
 }
 
-// AddAuthor adds the Person as an author to the Source.
-func (s *Source) AddAuthor(p *Person) {
-	if s.Authors == nil {
-		s.Authors = make([]*Person, 1)
-		s.Authors[0] = p
-	} else {
-		s.Authors = append(s.Authors, p)
-	}
+// AddAuthor adds the Person as an author to the Source. It returns an int.
+func (s *Source) AddAuthor(p *Person) int {
+	return addToSlice(&s.Authors, p)
 }
 
-// DeleteAuthor deletes the Person from the Source. It return an error.
-func (s *Source) DeleteAuthor(id int) error {
-	length := len(s.Authors)
-	if id > length {
-		return fmt.Errorf("error deleting author from source %v: id %v out of range %v", s, id, length)
+// DeleteAuthor deletes the Person at index from the Source. It return an error.
+func (s *Source) DeleteAuthor(index int) error {
+	if err := deleteFromSlice(&s.Authors, index); err != nil {
+		return fmt.Errorf("error deleting author %v from source %v: %v", index, s, err)
 	}
-
-	s.Authors = append(s.Authors[:id], s.Authors[id+1:]...)
 	return nil
 }
 
-// AddCategory adds the Category to the Source.
-func (s *Source) AddCategory(c *Category) {
-	if s.Categories == nil {
-		s.Categories = make([]*Category, 1)
-		s.Categories[0] = c
-	} else {
-		s.Categories = append(s.Categories, c)
-	}
+// AddCategory adds the Category to the Source. It returns an int.
+func (s *Source) AddCategory(c *Category) int {
+	return addToSlice(&s.Categories, c)
 }
 
-// DeleteCategory deletes the Category from the Source. It return an error.
-func (s *Source) DeleteCategory(id int) error {
-	length := len(s.Categories)
-	if id > length {
-		return fmt.Errorf("error deleting category from source %v: id %v out of range %v", s, id, length)
+// DeleteCategory deletes the Category at index from the Source. It return an
+// error.
+func (s *Source) DeleteCategory(index int) error {
+	if err := deleteFromSlice(&s.Categories, index); err != nil {
+		return fmt.Errorf("error deleting category %v from source %v: %v", index, s, err)
 	}
-
-	s.Categories = append(s.Categories[:id], s.Categories[id+1:]...)
 	return nil
 }
 
-// AddContributor adds the Person as a contributor to the Source.
-func (s *Source) AddContributor(c *Person) {
-	if s.Contributors == nil {
-		s.Contributors = make([]*Person, 1)
-		s.Contributors[0] = c
-	} else {
-		s.Contributors = append(s.Contributors, c)
-	}
+// AddContributor adds the Person as a contributor to the Source. It returns an
+// int.
+func (s *Source) AddContributor(c *Person) int {
+	return addToSlice(&s.Contributors, c)
 }
 
-// DeleteContributor deletes the Person from the Source. It return an error.
-func (s *Source) DeleteContributor(id int) error {
-	length := len(s.Contributors)
-	if id > length {
-		return fmt.Errorf("error deleting contributor from source %v: id %v out of range %v", s, id, length)
+// DeleteContributor deletes the Person at index from the Source. It return an
+// error.
+func (s *Source) DeleteContributor(index int) error {
+	if err := deleteFromSlice(&s.Contributors, index); err != nil {
+		return fmt.Errorf("error deleting contributor %v from source %v: %v", index, s, err)
 	}
-
-	s.Contributors = append(s.Contributors[:id], s.Contributors[id+1:]...)
 	return nil
 }
 
-// AddLink adds the Link to the Source.
-func (s *Source) AddLink(l *Link) {
-	if s.Links == nil {
-		s.Links = make([]*Link, 1)
-		s.Links[0] = l
-	} else {
-		s.Links = append(s.Links, l)
-	}
+// AddLink adds the Link to the Source. It returns an int.
+func (s *Source) AddLink(l *Link) int {
+	return addToSlice(&s.Links, l)
 }
 
-// DeleteLink deletes the Link from the Source. It return an error.
-func (s *Source) DeleteLink(id int) error {
-	length := len(s.Links)
-	if id > length {
-		return fmt.Errorf("error deleting link from source %v: id %v out of range %v", s, id, length)
+// DeleteLink deletes the Link at index from the Source. It return an error.
+func (s *Source) DeleteLink(index int) error {
+	if err := deleteFromSlice(&s.Links, index); err != nil {
+		return fmt.Errorf("error deleting link %v from source %v: %v", index, s, err)
 	}
-
-	s.Links = append(s.Links[:id], s.Links[id+1:]...)
 	return nil
 }
 
-// AddExtension adds the ExtensionElement to the Source.
-func (s *Source) AddExtension(e *ExtensionElement) {
-	if s.Extensions == nil {
-		s.Extensions = make([]*ExtensionElement, 1)
-		s.Extensions[0] = e
-	} else {
-		s.Extensions = append(s.Extensions, e)
-	}
+// AddExtension adds the ExtensionElement to the Source. It returns an int.
+func (s *Source) AddExtension(e *ExtensionElement) int {
+	return addToSlice(&s.Extensions, e)
 }
 
-// DeleteExtension deletes the Extension from the Source. It return an error.
-func (s *Source) DeleteExtension(id int) error {
-	length := len(s.Extensions)
-	if id > length {
-		return fmt.Errorf("error deleting extension from source %v: id %v out of range %v", s, id, length)
+// DeleteExtension deletes the Extension at index from the Source. It return an
+// error.
+func (s *Source) DeleteExtension(index int) error {
+	if err := deleteFromSlice(&s.Extensions, index); err != nil {
+		return fmt.Errorf("error deleting extension %v from source %v: %v", index, s, err)
 	}
-
-	s.Extensions = append(s.Extensions[:id], s.Extensions[id+1:]...)
 	return nil
 }