From: Trans <transfire@...>
Date: 2006-12-07T00:49:48+09:00
Subject: invasive parameters as method mode variables

Working on a method where I would like one part of it's operations to
be optional. Here's the crux of the code:

  def parse_multicommand( line=nil, arity={} )
    argv = parse_line(line)
    argv = multi_flag(argv)  # optional?

    # ...
  end

I would prefer not to add another parameter to the method signiture to
signify this option b/c its rare and it would complexify the call to
much, especially if there is more than one optional part --which is
possible. But other tahn that I don't have much choice, I'll probably
have to create an extra method called
#parse_multicommand_without_multi_flag. Yuk!

Not that helps me presently, but this did get me to thinking of using a
"global" flag that can be set external to the method. That would work
but it wouldn't be thread safe. Then it occured to me the
Binding.of_caller could be helpful here. Using the Binding#[] extension
for local variable access:

  def parse_multicommand( line=nil, arity={} )
    argv = parse_line(line)
    argv = multi_flag(argv) unless Binding.of_caller[:no_multi_flag]

    # ...
  end

Then to use:

  no_multi_flag = true
  parse_multicommand( line )

I know this breaks the whole idea of function encapsulation, but it has
it's advantages in certain cases like mine. It also might be of usedin
a few other places like String#each's separator. So that got me to
thinking of a cleaner way to provided this capability of invasive
parameters as "method mode variables".

  def parse_multicommand( line=nil, arity={} )
    argv = parse_line(line)
    argv = multi_flag(argv) unless --no_multi_flag

    # ...
  end

  # '--' indicates a method mode variable
  --no_multi_mode = true
  parse_multicommand( line ) 

Thouhgts?

T.