From: Thilanka Marasinghe <thilankaster@...>
Date: 2007-07-01T17:34:33+09:00
Subject: Re: newby non/programmer trying to understand classes

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hi
I Found this site very helpful when it came to understanding OO concepts for
Ruby
http://poignantguide.net/ruby

hope this is useful

On 6/30/07, Robert Klemme <shortcutter@googlemail.com> wrote:
>
>
> Hi,
>
> I believe Chris Pine's "Learning to program" has been suggested as an
> excellent introduction to OO programming.  You might want to have a look.
>
> My short introduction to OO programming would go like this: describe
> your problem in prose.  Identify important nouns, these are likely
> candidates for classes.  Then go from there and find out how they have
> to interact.
>
> On 29.06.2007 00:43, weathercoach@gmail.com wrote:
> >    Hello.
> >   Brief disclaimer.  I'm coming from a bourne shell back ground and
> > currently all of my ruby scripts look like shell scripts where I
> > create methods like i would a shell function and now that I understand
> > some of the language basics (variables, loops, exceptions) I want to
> > improve my skills and try to leverage the language instead of just
> > brute forcing my way through problems.    I'm not looking for a one
> > liner wizardry solution but some help getting a better understanding
> > of classes and ruby in general to change my approach to writing ruby
> > scripts.
> >
> >    I've scaled down my project to the most basic components that will
> > still allow me to express my areas of confusion.    I have a file that
> > changes daily which contains a list of people in this format
>
> So there we have the first noun that sounds like a candidate for a
> class: "people" (or as a singular "person").  Apparently a Person has at
> least two attributes, namely "last name" and "given name".
>
> You can create a person class pretty easily using Struct like this:
>
> Person = Struct.new :given_name, :last_name
>
> > bob.smith
> > bill.johnson
> > betty.joe
> > tony.johnson
> > wilbur.smith
> >
> >
> >    Additionally I have a directory populated with 1 file per uniq last
> > name (ie: smith, johnson, joe). I need to parse through the days list
> > and then cleanse the last name files of the previous entries and
> > insert the  updated list.     I've got the script that does this it is
> > not very efficient (ie: i must define all the last names in
> > advance).   So now i've started to rewrite the script and this is
> > where I'm stuck
>
> So this pretty much gives an outline of the algorithm:
>
> 1. read the updated list file and parse full names, remember persons in
> a smart way (for fast access)
>
> 2. read the list of surname files
>
> 3. delete all surname files where you do not have a person for
>
> 4. recreate all surname files
>
> Of course, other implementations would be possible.  If you go with this
> one way would be to create functions or methods for each of these steps
> above.
>
> You could, for example, place the reading of the name file into class
> Person as a class method:
>
> def Person.parse_persons(io)
>    persons = Hash.new {|h, k| h[k] = []}
>
>    io.each do |line|
>      if /^(\w+)\.(\w+)$/ =~ line
>        pers = new $1.lower, $2.lower
>        persons[pers.last_name] << pers
>      end
>
>    end
>    persons
> end
>
> This will return a Hash with last_names as keys and Person instances as
> values.  That way you retain all the information and can use it later
> for the file deletions and creations.
>
> Alternatively you could create a second class Persons and implement the
> parse method and all other methods in that class).  Maybe there is an
> even better way to do it - could be that we do not yet know the whole
> story and your script has to do other tasks as well.
>
> Just some food for thought.  HTH
>
> Kind regards
>
>         robert
>
>

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