Perl like anonymous subroutines in ruby

Question

I'm new to ruby and trying to duplicate this perl, that calls anonymous subroutines, in ruby:

#!/usr/bin/perl

use strict;
use warnings;
use feature 'say';

# Make a reference to a subroutine
my $codes = {
   one => sub {
      say "This is code block one";
      say "And this is code block one's line two"
   },
};

for my $next_code ( keys %{ $codes } ) {
   # Execute anonymous subroutine
   &{ $codes->{ $next_code } };
}

I tried this:

#!/usr/bin/ruby -w

codes = {
   one: puts "This is code block one"
        puts "And this is code block one's line two",
 }
codes.each do |next_code|
   next_code
end

But, I get syntax errors. Is this possible, or is there another preferred ruby way?

UPDATE: Yes, this is like a dispatch table. I store code in a hash and run that code later.

It looks like you might be trying to implement a dispatch table. If so, it would be good to mention that in your question to avoid the XY problem. There might be a better way to do it in Ruby that takes a completely different approach than Perl. — ThisSuitIsBlackNot
– ThisSuitIsBlackNot, Commented Jan 21, 2016 at 18:51
Can you explain in common words(not perl code) what do you want to do? — Maxim Pontyushenko
– Maxim Pontyushenko, Commented Jan 21, 2016 at 18:54
&{ $codes->{ $next_code } } is best written $codes->{ $next_code }->() — Borodin
– Borodin, Commented Jan 21, 2016 at 19:04

Jörg W Mittag · Accepted Answer · 2016-01-21 19:05:01Z

7

Ruby has Procs as anonymous first-class subroutine objects. Procs can be created by passing a block to Proc::new, Kernel#proc, or Kernel#lambda, or with the "stabby lambda" lambda literal syntax.

#!/usr/bin/env ruby

# Make a reference to a subroutine
codes = {
  one: -> {
    puts "This is code block one"
    puts "And this is code block one's line two"
  }
}

codes.each do |name, code|
  # Execute anonymous subroutine
  code.()
end

The most widely-used form of anonymous code block in Ruby is a construct called a block, which is actually not an object, but just a syntactic construct. Every method in Ruby takes exactly one optional block argument, which can be passed either in curly braces or using a do/end keyword pair after the normal method arguments. You can see a block in action in the code above, being passed to the Hash#each iteration method.

In case you are interested, here is a small toy project of mine that demonstrates the use of first-class closures in a variety of languages, including Perl5 and Perl6, Ruby, PHP, Python, ECMAScript, Smalltalk, Clojure, Scheme, and many others: http://joergwmittag.github.io/lambdaconscarcdr/

edited Jan 21, 2016 at 19:05

answered Jan 21, 2016 at 18:58

Jörg W Mittag

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2 Comments

Cary Swoveland Over a year ago

One thing interesting about procs is that they can be called in (at least?) five ways. Suppose f = ->s { puts "Say #{s}!" }. Then f.call('hey'), f['hey'], f.('hey'), f.yield('hey') and f === "hey" all print "Say hey!".

Jörg W Mittag Over a year ago

Although the "normal" way is to use call or its syntactic sugar .(). [] is an outdated alias for call that was used to make calling a Proc more like a method call by using the brackets as fake parentheses. As of Ruby 1.9, we have the .() notation, which serves this purpose better, IMO. yield I didn't know about, I suppose it is for API compatibility with Fibres? === is useful for using Procs in case expressions and Enumerable#grep, but probably shouldn't be called directly. Note: all of them are aliases for call, except (), which is syntax sugar for call.

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