From: Adam Shelly <adam.shelly@...>
Date: 2008-01-31T10:20:16+09:00
Subject: Re: Idiomatic way to copy parameters ?

On 1/30/08, Leif Eriksen <leif.eriksen@bigpond.com> wrote:
>
>  def self.gradient(hex_start="000000", hex_end="FFFFFF", steps=256)
>      [hex_start,hex_end].each do |hex|
>         hex.sub!(/^(0[xX]|#)/) do |match|
>           match = '' # remove any leading # or Ox
>
> So the strings that are passed in are permanently munged by the sub! .
> OK I get that, and to solve it I did this
>
>  def self.gradient(param_start="000000", param_end="FFFFFF", steps=256)
>    #make local copies of parameters
>    hex_start = String.new(param_start)
>    hex_end   = String.new(param_end)
>
>      [hex_start,hex_end].each do |hex|
>        hex.sub!(/^(0[xX]|#)/) do |match|
>        ...
>
> So in effect I copy the parameter strings into local vars, to avoid
> munging what the user passes me and annoying them.
>
> But is this the ruby way ? Is this the idiomatic way to avoid
> side-effects on objects passed in as parameters ?
>

I'm no idiom expert, but I'd say no.  You are correct that if you are
going to do a destructive operation without affecting the caller, you
need to make a copy.  But usually, it's simpler to just get a modified
copy by calling the non-destructive version:


def self.gradient(hex_start="000000", hex_end="FFFFFF", steps=256)
   hex_start=hex_start.gsub(/^(0[xX]|#)/,'')
   hex_end=hex_end.gsub(/^(0[xX]|#)/,'')
...
end

-Adam