Re: Understanding Ruby blocks

2011/11/24 Jes=FAs Gabriel y Gal=E1n <[e-mail]>:
> On Thu, Nov 24, 2011 at 4:55 PM, Fily Salas <[e-mail]> wrote:
>> 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?

To make the code robust and ensure the resource is freed under all
circumstances (especially exceptions, but also control flow which uses
break, return or throw).

> 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.

Shameless self advertizing: More explanations here:

http://blog.rubybestpractices.com/posts/rklemme/001-Using_blocks_for_Robust=
ness.html
http://blog.rubybestpractices.com/posts/rklemme/002_Writing_Block_Methods.h=
tml

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

Yep, a block is just an anonymous function with a nice invocation
syntax.  In other programming languages one _sometimes_ uses template
method pattern in such situations
http://en.wikipedia.org/wiki/Template_method_pattern

Kind regards

robert

--=20
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/