Argument passing with |boofar| (fwd)

ruby-talk
1

There are two ways to use File.open:
1) the one you may be familiar with, like

my_file = File.open("songdata")
s = my_file.read
my_file.close

2) the second that takes a block

File.open("songdata") do |my_file|
  s = my_file.read
end

#open calls the block only one time (there is
nothing to iterate here) passing in the file object
it would have returned if called without the block.

Why? because it's a nice way of resource handling.
After calling the block #open closes the file. You
can't forget to call close.

cheers

Simon

···

-----Original Message-----
From: Jurgen Stroo [mailto:blurg@JurgenStroo.com]
Sent: Thursday, September 22, 2005 10:16 AM
To: ruby-talk ML
Subject: Argument passing with |boofar| (fwd)

Lo Fellow listers,

I already mentioned I am starting to learn Ruby the last
couple of days.
I came across the following in the Prog. Ruby book:

File.open("songdata") do |song_file|
  songs = SongList.new
  song_file.each do |line|
      file, length, name, title = line.chomp.split(/\s*|\s*/)
    songs.append(Song.new(title,name,length))
  end
  puts songs[1]
end

I previously read about the argument passing between methods and code
blocks. They used explanations of this construct which were
indeed clear
to me:

('a'..'e').each {|char| print char}

this each method is of course iterating over the list and
returning the
value each time for each list entry, which is passed as the variable
'char' in the block. (correct me if I'm wrong)

But, in the case of:

  File.open("songdata") do |song_file|

what is returned then? I mean, the File.open is just a
statement without a
return value, or isn't it?

I hope someone can explain me the inner workings of the given example
which is not clear to me.

Many thanks,
Jurgen

2

Thanks Jeremy and Simon,

Things are clear to me now.

Although very unlikely, it seems Kroeger Simon (ext) stated on Sep 22 that :

···

There are two ways to use File.open:
1) the one you may be familiar with, like

my_file = File.open("songdata")
s = my_file.read
my_file.close

2) the second that takes a block

File.open("songdata") do |my_file|
  s = my_file.read
end

#open calls the block only one time (there is
nothing to iterate here) passing in the file object
it would have returned if called without the block.

Why? because it's a nice way of resource handling.
After calling the block #open closes the file. You
can't forget to call close.

cheers

Simon

> -----Original Message-----
> From: Jurgen Stroo [mailto:blurg@JurgenStroo.com]
> Sent: Thursday, September 22, 2005 10:16 AM
> To: ruby-talk ML
> Subject: Argument passing with |boofar| (fwd)
>
> Lo Fellow listers,
>
> I already mentioned I am starting to learn Ruby the last
> couple of days.
> I came across the following in the Prog. Ruby book:
>
> File.open("songdata") do |song_file|
> songs = SongList.new
> song_file.each do |line|
> file, length, name, title = line.chomp.split(/\s*|\s*/)
> songs.append(Song.new(title,name,length))
> end
> puts songs[1]
> end
>
> I previously read about the argument passing between methods and code
> blocks. They used explanations of this construct which were
> indeed clear
> to me:
>
> ('a'..'e').each {|char| print char}
>
> this each method is of course iterating over the list and
> returning the
> value each time for each list entry, which is passed as the variable
> 'char' in the block. (correct me if I'm wrong)
>
> But, in the case of:
>
> File.open("songdata") do |song_file|
>
> what is returned then? I mean, the File.open is just a
> statement without a
> return value, or isn't it?
>
> I hope someone can explain me the inner workings of the given example
> which is not clear to me.
>
> Many thanks,
> Jurgen
>
>
>