Examples of implementing Type Classes in Scala

TypeClassExamples.scala

trait Publishable {
	def asWebMarkup: String
}

case class BlogPost(title: String, text: String) extends Publishable {
	def asWebMarkup = 
		"""|<h2>%s</h2>
		   |<div>%s</div>""".stripMargin format(title, text)
}

class WebPublisher[T <: Publishable] {
	def publish(p: T) = println(p.asWebMarkup)
}

val post = new BlogPost("Test", "This is a test post")
val web = new WebPublisher[BlogPost]()
web publish(post)

//////////////////////////////////////////////////////////////////////////////

trait Publishable {
	def asWebMarkup: String
}

case class BlogPost(title: String, text: String)

implicit def BlogPostToPublishable(blogPost: BlogPost) = new Publishable {
	def asWebMarkup = 
		"""|<h2>%s</h2>
		   |<div>%s</div>""".stripMargin format(blogPost title, blogPost text)
}

class WebPublisher[T <% Publishable] {
	def publish(p: T) = println(p.asWebMarkup)
}

val post = new BlogPost("Test", "This is a test post")
val web = new WebPublisher[BlogPost]()
web publish(post)

//////////////////////////////////////////////////////////////////////////////

trait Publishable[T] {
	def asWebMarkup(p: T): String
}

case class BlogPost(title: String, text: String)

object BlogPostPublisher extends Publishable[BlogPost] {
	def asWebMarkup(p: BlogPost) = 
		"""|<h2>%s</h2>
		   |<div>%s</div>""".stripMargin format(p title, p text)
}

implicit def Publishable[BlogPost] = BlogPostPublisher

class WebPublisher[T: Publishable] {
	def publish(p: T) = println(implicitly[Publishable[T]] asWebMarkup(p))
}

val post = new BlogPost("Test", "This is a test post")
val web = new WebPublisher[BlogPost]()
web publish(post)