overloading evaluation (treating objects as functions)

[dan via Digitalmars-d-learn]

Is it possible to define a class F so that
     auto f=new F();
     writeln("The value of f at 7 is ",f(7));
compiles and works as expected?

So the idea would be to be able to use notation like
     f(7)
instead of
     f.eval(7)
or something along those lines.

My guess is no, it is impossible to do this, because i can't find 
it on the internet or in Alexandrescu's book.

But it is also possible that everybody considers it so obvious 
that they just don't elaborate on it.  I'd be delighted if there 
were the case, at least if somebody would elaborate on it if so.

TIA for any info!

dan