Anonymous function as argument in scala

Question

In Play 2.3, the Action.async method has the signature

final def async(block: ⇒ Future[Result]): Action[AnyContent]

I did not figure out the meaning of => Future[Result], is it an anonymous function? Then shouldn't it be () => Future[Result]?

You can find your answer here: http://stackoverflow.com/questions/22670356/scala-passing-function-as-block-of-code-between-curly-braces and in many other similar questions. — Łukasz, Dec 17 '15 at 09:14

score 2 · Accepted Answer · edited May 23 '17 at 11:44

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It is a "By-name parameter":

edited May 23 '17 at 11:44

Community

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answered Dec 17 '15 at 09:19

Filippo Vitale

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score 0 · Answer 2 · answered Dec 17 '15 at 09:27

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This is a call by name not by value as usual. It means, the argument, here block is of Type Future[Result] and it is lazy evaluated when needed not instantly on function call.

answered Dec 17 '15 at 09:27

Guenter Guckelsberger

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it's a subtler difference than "lazily evaulated" - http://stackoverflow.com/q/13337338/409976. – Kevin Meredith Dec 17 '15 at 12:42

Anonymous function as argument in scala

2 Answers2