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comp.lang.ruby

About blocks

Surgeon

1/2/2006 11:48:00 AM

Hi,

(This question might be answered previously. If so, I apologize.)

Can we *ALWAYS* use plain methods instead of blocks? Yes, sometimes
using a block may be obviously better than using a method but I mean,
are there any situations in which the *ONLY* solution is to use a block
rather than a method? May someone be forced to use only and only a
block? I ask this because I am not very intelligent and I am not sure
that I will thoroughly understand the "block" concept.
2 Answers

Robert Klemme

1/2/2006 1:19:00 PM

0

Surgeon <biyokuantum@gmail.com> wrote:
> Hi,
>
> (This question might be answered previously. If so, I apologize.)
>
> Can we *ALWAYS* use plain methods instead of blocks? Yes, sometimes
> using a block may be obviously better than using a method but I mean,
> are there any situations in which the *ONLY* solution is to use a
> block rather than a method? May someone be forced to use only and
> only a block? I ask this because I am not very intelligent and I am
> not sure that I will thoroughly understand the "block" concept.

You need blocks everywhere you need an anonymous callback function such as
with iterations:

an_array.each {|e| ... }

And you need lambdas (i.e. blocks converted to an object) if you need to
store the thing in a variable:

class SortedArray < Array
attr_accessor :comparator
def each
sort!(&comparator)
super(&b)
end
end

Does that help?

Kind regards

robert

Michael 'entropie' Trommer

1/2/2006 7:57:00 PM

0

* dblack@wobblini.net (dblack@wobblini.net) wrote:
> Hi --
>
> On Mon, 2 Jan 2006, Surgeon wrote:
>
> >Hi,
> >
> >(This question might be answered previously. If so, I apologize.)
> >
> >Can we *ALWAYS* use plain methods instead of blocks? Yes, sometimes
> >using a block may be obviously better than using a method but I mean,
> >are there any situations in which the *ONLY* solution is to use a block
> >rather than a method? May someone be forced to use only and only a
> >block? I ask this because I am not very intelligent and I am not sure
> >that I will thoroughly understand the "block" concept.
>
> You don't really use methods instead of blocks; you use methods --
> that is, you call methods -- with or without providing a code block
> for a given method call.
>
> The block is part of the method call syntax, along with the method
> name and the argument list. Whether or not it's mandatory is up to
> the method (as with arguments). For example:
>
> def x
> end
>
> def y
> yield
> end
>
> def z
> yield if block_given?
> end
>
> x # OK -- no block expected or given
> x { puts "code block" } # block OK but ignored
>
> y # error, because no block to yield to
> y { puts "code block" } # OK
>
> z # OK -- no yield will be attempted
> z { puts "code block" } # also OK, and block will execute
>
>
> David

really intresting lecture!

>
> --
> David A. Black
> dblack@wobblini.net
>
> "Ruby for Rails", from Manning Publications, coming April 2006!
> http://www.manning.com/b...
>
So long
--
Michael 'entropie' Trommer; http:/...

ruby -e "0.upto((a='njduspAhnbjm/dpn').size-1){|x| a[x]-=1}; p 'mailto:'+a"