From: Sean O'Dell <sean@...>
Date: 2003-07-18T02:37:57+09:00
Subject: Re: What's the point?

"Jim Freeze" <jim@freeze.org> wrote in message
news:20030717103702.A3418@freeze.org...
> Hi
>
> I've known for some time that methods can be defined inside
> methods, but I am still wondering what's the point.
>
>   def fred
>     def x
>       puts "x"
>     end
>     x
>   end
>
>   fred
>   x
>
> produces
> x
> x
>
> Why would any sane person do such a thing? :)

They're known as "local functions" I think (not sure if that is a universal
term for them).  I use these from time to time in Pascal.  I have several
uses for them:

1) To "tuck away" code in a function which makes the function hard to
follow.  For example, if a "for" statement has 15 lines of code in it
(making code before and after the for statement spread apart), I might put
all that code up into a local function and the for statement will just call
it.  The code itself isn't particularly re-usable, so I leave it out of the
parent function's namespace and keep it in a local function.

2) Same as #1, but especially when I call the same code from more than one
place in a function, and it's, again, not particularly re-usable.

If the code ever hints at re-usability, then I find it a real home in a
namespace somewhere.

3) To override other functions temporarily (perhaps even permanently).  This
is a bit like Aspect programming, I think.  For example, if a function I've
written calls printf, but for a test I want all the data being printed to go
to both a file for logging purposes and to a TCP/IP connection for remote
logging, I could write a local function called printf.  Being able to
re-define a function on-the-fly for quick debugging purposes is very nice.

I like the fact that Ruby has local functions.  It's mainly a procedural
programming device, but personally, while I love Ruby's pure-OOP-ness, I
think it's wise to also incorporate other programming idioms.

    Sean O'Dell