CODEWITHSUNDEEP
scala
woof-woof
woof-woof

Reputation: 607

Instantiation of Play! Action - what language construction is that?

What language construction is used here to create Action instance? I thought that in Scala it is possible to instantiate a class using:

But in the Scaladoc of Play! Action is see following snippet:

val echo = Action { request =>
  Ok("Got request [" + request + "]")
}

What is called here? I understand that we create function request => response, but where is this function passed?

Upvotes: 1

Views: 149

Answers (3)

Alexander Arendar
Alexander Arendar

Reputation: 3435

To all said above, for you also would be useful to CTRL + click on the class/method name in your IDE and look in the source code. That sometimes clarifies a lot. Please try and you will see 3 or 4 different variants of apply() methods in the ActionBuilder class.

Upvotes: 0

smartnut007
smartnut007

Reputation: 6423

Basically you are calling the Action companion object's apply method. And as Andreas pointed out during method calls () can be replaced by {} AFAIK.

api doc Action object

def apply(block: (Request[AnyContent]) ⇒ Result): Action[AnyContent]

Action is a subclass of ActionBuilder. It goes to this method call in the play frame work source code.

Upvotes: 2

user500592
user500592

Reputation:

Your example is equivalent to this:

val echo = Action.apply(request => Ok("Got request [" + request + "]"))

So you're actually calling object Action's apply method and pass it an anonymous function.

Be aware that in Scala, you can mostly interchange parentheses and braces, so e.g. if you have this function

def f(a: Int) = a + 42

these calls are equivalent:

f(23)
f { 23 }

The next thing that happens is that you can omit the name of the apply method. So if you have an object like this:

object f { def apply(a: Int) = a + 42 }

these calls are all equivalent:

f.apply(23)
f.apply { 23 }
f(23)
f { 23 }
f apply 23
f apply { 23 }

Upvotes: 5

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