Re: Array#and? and Array#or? methods

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Thanks for pointing out Enumerable#detect.  I just started looking at 
Ruby this week, and didn't think to look at methods other than in Array!

detect seems to work easily for the "or?" case:

  def even?(n)
    (n&1) 0
  end

  [1,2,3].detect {|x| even? x}   2

(except that it returns the element found, rather than true or false, 
which causes a problem if the found element is nil!)

For the "and?" case it is a bit awkward, though, because you have to "de 
Morgan" the result and your test by negating them:

  ! [2,4,6].detect {|x| ! even? x}   true

It sounds like Ruby 1.7 has what I want (except named all? and any?, but 
that is okay ;^)

Thanks for the comments!

[BTW, I had to send/edit this reply twice to get it past SpamAssassin, 
who kept rejecting it as spam!]


dblack / candle.superlink.net wrote:

>Hi --
>
>On Thu, 28 Nov 2002, Jeff de Vries wrote:
>
>  
>
>>Is there some reason the following methods on Array aren't included as
>>standard?
>>
>>class Array
>>  def and?
>>    # return true if the provided block returns true for every element
>>    each {|x| return false unless yield x} if block_given?
>>    return true
>>  end
>>  def or?
>>    # return true if the provided block returns true for at least one
>>element
>>    each {|x| return true if yield x} if block_given?
>>    return false
>>  end
>>end
>>
>>I find these to be very useful, and was suprised to not see them.  Is
>>there another way to get the same effect (including short circuit of
>>evaluation as soon as a condition fails)?
>>    
>>
>
>Yes, you can use detect:
>
>  a  1,2,3,4]
>  a.detect {|e| e 2}
>
>and just use the logic however you need it:
>
>  puts "failure" unless a.detect {|e| e 3}
>
>etc.  (For simple cases like this you can also use include? )
>
>
>David
>
>  
>


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<div classoz-text-html" lang-western">      Thanks for pointing out
Enumerable#detect. &nbsp;I just started looking at Ruby this week, and didn't think
to look at methods other than in Array!<br>
<br>
detect seems to work easily for the "or?" case:<br>
<tt><br>
&nbsp; def even?(n)<br>
&nbsp; &nbsp; (n&amp;1) 0<br>
&nbsp; end<br>
<br>
&nbsp; [1,2,3].detect {|x| even? x} &nbsp;gt; 2<br>
<br>
</tt>(except that it returns the element found, rather than true or false,
which causes a problem if the found element is nil!)<br>
<br>
For the "and?" case it is a bit awkward, though, because you have to "de
Morgan" the result and your test by negating them:<br>
<br>
<tt>&nbsp; ! [2,4,6].detect {|x| ! even? x} &nbsp;gt; true<br>
<br>
</tt>It sounds like Ruby 1.7 has what I want (except named all? and any?,
but that is okay ;^)<br>
<br>
Thanks for the comments!<br>
<br>
[BTW, I had to send/edit this reply twice to get it past SpamAssassin, who
kept rejecting it as spam!]<br>
<br>
<br>
<a classoz-txt-link-abbreviated"
 hrefailto:dblack / candle.superlink.net">dblack / candle.superlink.net</a>
wrote:<br>
<blockquote typeite"
 citeidPine.LNX.4.44.0211271221590.5760-100000 / candle.superlink.net">
  
  <pre wrap>Hi --

On Thu, 28 Nov 2002, Jeff de Vries wrote:

  </pre>
     
  <blockquote typeite">         
    <pre wrap>Is there some reason the following methods on Array aren't included as
standard?

class Array
  def and?
    # return true if the provided block returns true for every element
    each {|x| return false unless yield x} if block_given?
    return true
  end
  def or?
    # return true if the provided block returns true for at least one
element
    each {|x| return true if yield x} if block_given?
    return false
  end
end

I find these to be very useful, and was suprised to not see them.  Is
there another way to get the same effect (including short circuit of
evaluation as soon as a condition fails)?
    </pre>
  </blockquote>
     
  <pre wrap><!---->
Yes, you can use detect:

  a  1,2,3,4]
  a.detect {|e| e 2}

and just use the logic however you need it:

  puts "failure" unless a.detect {|e| e 3}

etc.  (For simple cases like this you can also use include? )


David

  </pre>
</blockquote>
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