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Suppose I have defined a function:

def hello(name:String, words:String) = println("Hello!" + name + words)

Then I defined a partial function:

def p = hello _

Print p, displayed:

(String, String) => Unit = <function2>

There's no function name displayed. Is it possible to get the original method name hello from the partial function p?

hammar
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Freewind
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  • Edited "partial function" to "partially applied function" in the tag and question title, so that the appropriate people will be attracted to (or repelled from) this question. – Rex Kerr Mar 21 '11 at 18:28
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    To add to Rex's comment, a "partial function" is a function that is not defined for all input in its domain type. The cannonical partial function is something like def f(x : Int) = 1/x. Scala also has a PartialFunction trait that function objects may implement if they want to answer a query indicating where they are and are not defined. Neither concept should be confused with partial application. – James Iry Mar 21 '11 at 20:59

3 Answers3

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There has been some discussion on the mailing lists recently about a language construct that allows you to identify the current method that you're in. It would be called something like thisMethod and would essentially do for methods what this does for class instances.

I'd be interested to see how this interacts with functions (which are a different concept from methods). Your p is an anonymous function created from partially applying the hello method (again, you need to be careful here, a "partially applied function is a very different thing from a PartialFunction). The actual method then invoked would be apply on this function object, and there are several possibilities as to how thisMethod could behave in such a case.

Whatever happens, p is just an object reference, don't expect to ever be able to access it as a name.

Kevin Wright
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No.

Its a feature I'd love to have, but it has serious conceptual problems like, what should happen, when the same function is given two names ... it should still be the same function, shouldn't it?

update in response to comment:

def p = hello _ def q = p

What is the name of q? p? or hello? or println? I have a hard time imagining a solution that is simple, consistent and usefull.

Jens Schauder
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  • thanks! But I don't understand how the function is given two names? I hope there is a method say `getOriMethodName` that returns `hello`, will this cause some problems? Sorry I'm a newbie to scala. – Freewind Mar 21 '11 at 15:13
  • Formally speaking, we don't write functions we write procedures that compute functions. def f(x : Int) = 2 * x and def g(x : Int) = x + x are two different procedures that compute the same function. But that's just pedantry and I think this answer should not be voted up because it's besides the point of what's being asked for - a debugging tool. – James Iry Mar 21 '11 at 21:01
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... that is actually a "partially applied function" that is created anonymously by calling your hello function without the parameters being applied. It does not have an explicit name to show.

scaling_out
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