Create a method that receives a type parameter but not as a parameter, just like classOf

Question

I have the following code:

class ServletSpec extends Specification {

    def createServlet[T <: HttpServlet](clazz: Class[T]): T = {

        val instance = clazz.newInstance()
        instance.init()

        instance

    }

}

That is called like this:

spec.createServlet( classOf[DocumentationServlet] )

How can I define this method so that I can call it like this:

spec.createServlet[DocumentationServlet]

score 5 · Accepted Answer · edited May 23 '17 at 12:27

5

Using Manifests:

class ServletSpec extends Specification {
    def createServlet[T <: HttpServlet]()(implicit manifest: Manifest[T]) = {
        val instance = manifest.erasure.newInstance().asInstanceOf[T]
        instance.init()

        instance
    }
}

new ServletSpec().createServlet[DocumentationServlet]()

The implicit parameter is filled in by the compiler, and a Manifest contains the type information required to create a new instance. For more information, see What is a Manifest in Scala and when do you need it?

edited May 23 '17 at 12:27

Community

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answered Nov 29 '11 at 19:52

Matthew Farwell

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Not working for me, manifest.erasure is of Class[_] instead of Class[HttpServlet]. Am I missing something here? – Maurício Linhares Nov 29 '11 at 19:59
Sorry, missed off the .asInstanceOf, see val instance line – Matthew Farwell Nov 29 '11 at 20:03
Hum, so I have to cast the value to what I want as the manifest is not going to be of the exact type? Nice, thank you! – Maurício Linhares Nov 29 '11 at 20:03

Create a method that receives a type parameter but not as a parameter, just like classOf

1 Answers1