Re: Understanding Ruby blocks

On Thu, Nov 24, 2011 at 4:55 PM, Fily Salas <[e-mail]> wrote:
> Hi,
>
> I have been practicing Ruby and believe it or not the hardest part for
> me to understand (so far) is the concept of using blocks, why used them
> and how to use them.

There are several benefits and use cases for using blocks.

> For instance, I know I don't fully understand blocks but why would you
> use a block in the following situation.
>
> text =3D "Some Text"
> File.open('test_file.txt', 'a+') do |file|
> =A0 file.write(text)
> end
>
> Why not just ...?
>
> text =3D "Some Text"
> =A0file =3D File.open('test_file1.txt', 'a+')
> file.write(text)
> ..why use a block instead?

This is quite straightforward: in this situation the use case is that
you want to ensure that something happens before and after the block
code. In this case, the File#open method opens the file, then calls
the block and then ensures that the file is closed, even in the face
of an exception within the block.

So, first use case: when you want code executed around code that is
not under your control.

Another use case is when you provide a generic functionality that can
applied to many situations, but you want to leave the exact detailed
behavior to the client code. For example, the Enumerable#each method
provides its clients with the capability of traversing an enumerable
instance, doing something with each element one at a time. What you do
with the element is responsibility of the client code, so the each
method just accepts a block to achieve that.

Hope this helps and I hope the concept clicks soon, because it's one
of the things that make Ruby so wonderful.

Jesus.


> 1-What would be a good rule of thumb to know when to use blocks?
> 2-What would be the easiest way to understand block?
> 3-Can someone be so kind and explain block a little bit?
>
> Thanks a lot for all of your help!
> Learning a lot in this forum. Awesome people!
>
> --
> Posted via http://www.ruby-forum.com/.
>
>