捕获按名称呼叫参数的表示形式

Question

I'm trying to print the call-by-name argument passed to a function, that is:

def testme(arg: => Int) println(arg)

And call it like so:

test(sum(List(1, 2, 3))

Provided that sum method exists. I want testme to print sum(List(1, 2, 3)) and not the sum itself.

Is there a way to achieve this?

Answer 1

No, it's not possible without hacking the compiler. When you're passed f: => A, calling f evaluates it immediately. It isn't ever in an intermediate form of the type you would like, because scala is compiled down to java byte code, not interpreted like a scripting language.

Edit: As Regis points out, hacking the compiler is easier than in some languages because scala exposes an api to the compiler, via scala macros. It is still fairly complicated, and you are probably better off figuring out your solution another way.