Object#methods_returning - to work out which method on an object returns what we want

methods_returning.rb

require 'stringio'
require 'timeout'

class Object
  def methods_returning(expected, *args, &blk)
    old_stdout = $>
    $> = StringIO.new

    methods.select do |meth|
      Timeout::timeout(1) { dup.public_send(meth, *args, &blk) == expected rescue false } rescue false
    end
  ensure
    $> = old_stdout
  end
end

# ----------------

p [1, nil, 'x'].methods_returning [1, 'x']
           # => [:compact, :compact!]

p [1, 2, 3].methods_returning [3, 2, 1]
           # => [:reverse, :reverse!]

p [1, 2, 3].methods_returning []
           # => [:values_at, :clear, :singleton_methods, :protected_methods, :instance_variables]

p [1, 2, 3].methods_returning([2, 4, 6]) { |i| i * 2 }
           # => [:collect, :collect!, :map, :map!, :flat_map, :collect_concat]

p [1, 2, 3].methods_returning('123')
           # => [:join]

p (1..5).methods_returning([[1, 3, 5], [2, 4]], &:odd?)
           # => [:partition]

p 'A'.methods_returning 'a'
           # => [:downcase, :swapcase, :downcase!, :swapcase!]

This is a novel idea for finding library methods if you're unfamiliar with its methods - helps you narrow your focus before you dive into the doc/code. I think I'll try this next time I use a new gem, though I suspect it could still be useful for stdlib type stuff. Nice one!

This might be a good addition to Pry.

Here's something I always forget:

irb [1.9.3]$ 10.methods_returning [3,1], 3
=> []

But the dup + rescue false is not helping me remember... 😄

https://github.com/citizen428/methodfinder is similar, written starting about 3 years ago.

How long until someone manages to wipe out their filesystem by using this on the wrong object? :-P

@kotp 👍

+1

I thought I'd seen this idea somewhere before, kotp - good find!

there is a similar thing in Smalltalk