From: Robert Klemme <bob.news@...>
Date: 2005-08-10T21:06:10+09:00
Subject: Re: passing a method

Wybo Dekker wrote:
> Patrick Gundlach and Devin Mullans wrote:
>
>  > @t = ''
>  > def bye
>  >   @t << 'bye'
>  > end
>  > def hello
>  >   @t << 'hello'
>  > end
>  > def doit(f)
>  >   send f
>  > end
>  > doit(:hello)
>  > doit(:bye)
>  > doit(:hello)
>  > puts @t
>
> That's exactly what I needed. Thanks!
>
> As for daniel's question:
>
>  > Why do you want to do this?
>
> and
>
>  > This is a rather poor example, since the above three lines
>  > could just as well be written like this:
>
>  >   hello
>  >   bye
>  >   hello
>
> Of course, that's because an exmaple should be short.
> My actual code is an initializer for my scripts. I find myself all the
> time re-inserting, in many scripts, code to test if executables are
> available, code to read rc-files, to handle options, and more. I want
> to put most of that stuff in a module which now contains an init
> method using the above suggestion (for the last argument):
>
> # program initializer:
> # 1. check if all needed executables (in _needed_) are available
> # 2. set the defaults (values of _defaults_) for
> #    option- and rc-variables (keys of _defaults_)
> # 3. read the standard rc-files
> # 4. handle the options, as defined in the _optionproc_ method
> # 5. if @rc appears to be defined, read it as an rc-file
>
> def init(needed,defaults,option_handler)
>    @rcfiles = [] # collect names for a report in case @verbose is true
>
>    # set defaults:
>    defaults.each do |k,v|
>       eval("@#{k} = #{v || 'nil'}")
>    end
>
>    # check if all needed executables (in _needed_) are available
>    check_execs(needed)
>
>    # run all standard rc-files
>    read_rc_files(defaults.keys)
>
>    # handle options
>    send option_handler
>
>    # in case a --rc option was used, read its argument as an rc-file:
>    read_rc_file(@rc,defaults.keys)
>
>    # if the --verbose option was used, report rc-files read:
>    if @verbose
>       if @rcfiles.size > 0
>          puts "These rc files were read:",@rcfiles.join("\n")
>       else
>          puts "No rc files were read"
>       end
>    end
> end

IMHO a superior solution would be to use a block instead of argument
option_handler.  AFAICS you have only one such callback and that's exactly
what blocks are for.  If you want access to the current instance you can
use instance_eval:

def init(needed,defaults,&option_handler)
....
   # handle options
   instance_eval &option_handler
....
end

Also, for setting instance variables, this idiom is better (because it
avoids evil eval and you don't need special handling of nil):

defaults.each {|k,v| instance_variable_set("@#{k}", v)}

Kind regards

    robert