Question

Let’s assume this function:

def autoClosing(f: {def close();})(t: =>Unit) = {
    t
    f.close()
}

and this snippet:

val a = autoClosing(new X)(_)
a {
 println("before close")
}

is it possible to curry the first part? Something like:

val a = autoClosing(_) { println("before close") }

so that I could send the objects on which close should be performed, and have the same block executed on them?

Answer 1

Yes, the snippet you have given works, as long as you give the type of the placeholder character.

Therefore, the code you are looking for is:

val a = autoClosing(_: {def close();}) { println("before close") }

which compiles and works as expected :).

A couple of notes:

• You can make your life easier if you define a type alias for an AnyRef type having a close method, something like type Closeable = AnyRef {def close()}, or an appropriate interface.
• The code snippet autoClosing(_: Closeable){ ... } is actually equivalent to the following expanded anonymous function: c: Closeable => autoClosing(c){ ... }. The wildcard character is just shorthand for a partially applied function. You need to give the type of the _ as the type inferer unfortunately cannot infer the type in this case.

Hope it helps,

— Flaviu Cipcigan