Is there a more concise way to call an outside method on a map in Ruby?

Question

Is there a more concise way of doing this?

# Given a directory containing subdirectories: foo, bar
targets = ['./foo', './bar', './free']
targets.map{ |d| Dir.exists? d }
# => [ true, true, false ]

I'd love to be able to do something similar to proc calls... it feels cleaner:

# targets.map( Dir.exists? )

score 4 · Accepted Answer · edited May 23 '17 at 11:50

4

Yes, possible this way, but not good for performance (see post: Is the &method(:method_name) idiom bad for perfomance in Ruby?):

targets = ['./foo', './bar', './free']
targets.map(&Dir.method(:exists?))
# => [false, false, false]  #all are false,as I don't have such directories.

edited May 23 '17 at 11:50

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answered Sep 15 '13 at 19:36

Arup Rakshit

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What exactly did you mean by "point-free"? :) – Sergio Tulentsev Sep 15 '13 at 19:40
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This is awesome. Can you explain the process (no pun intended)? Fascinating! – Jason Sep 15 '13 at 19:41
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I personally think that the original version reads better (by far). But it's good to have more than one way to do things. – Sergio Tulentsev Sep 15 '13 at 19:41
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@SergioTulentsev See here - http://stackoverflow.com/questions/6976629/is-the-methodmethod-name-idiom-bad-for-perfomance-in-ruby/7169467#7169467 and http://stackoverflow.com/questions/6962883/how-to-unflatten-a-ruby-array/6963422#6963422 – Arup Rakshit Sep 15 '13 at 19:43
@Babai: so, you see, in those examples there are no points(dots). But in yours there is one :) – Sergio Tulentsev Sep 15 '13 at 19:45
@SergioTulentsev Humm.. I did notice.. But here I need to put the point :) Thanks for pointing me to the point. – Arup Rakshit Sep 15 '13 at 19:47
Also, it's bad for performance. So it shouldn't be used. – Sergio Tulentsev Sep 15 '13 at 19:47
@JasonTFeatheringham The link I put in the comment in the answers has the answer,for you.. Please look into those. – Arup Rakshit Sep 15 '13 at 19:47
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Just did. Excellent information. Wish I could up the answer more than once :) – Jason Sep 15 '13 at 19:48
@SergioTulentsev put the same in my answer too. I was going to give that,but got busy to answer you..:) – Arup Rakshit Sep 15 '13 at 19:50
I confirmed it's bad for performance in MRI Ruby 2.0.0. It takes twice as long to do it this way. – davogones Sep 15 '13 at 22:38

Is there a more concise way to call an outside method on a map in Ruby?

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