Can you supply arguments to the map(&:method) syntax in Ruby?

by

You can create a simple patch on Symbol like this:

class Symbol
  def with(*args, &block)
    ->(caller, *rest) { caller.send(self, *rest, *args, &block) }
  end
end

Which will enable you to do not only this:

a = [1,3,5,7,9]
a.map(&:+.with(2))
# => [3, 5, 7, 9, 11]

But also a lot of other cool stuff, like passing multiple parameters:

arr = ["abc", "babc", "great", "fruit"]
arr.map(&:center.with(20, '*'))
# => ["********abc*********", "********babc********", "*******great********", "*******fruit********"]
arr.map(&:[].with(1, 3))
# => ["bc", "abc", "rea", "rui"]
arr.map(&:[].with(/a(.*)/))
# => ["abc", "abc", "at", nil] 
arr.map(&:[].with(/a(.*)/, 1))
# => ["bc", "bc", "t", nil]

And even work with inject, which passes two arguments to the block:

%w(abecd ab cd).inject(&:gsub.with('cde'))
# => "cdeeecde"

Or something super cool as passing [shorthand] blocks to the shorthand block:

[['0', '1'], ['2', '3']].map(&:map.with(&:to_i))
# => [[0, 1], [2, 3]]
[%w(a b), %w(c d)].map(&:inject.with(&:+))
# => ["ab", "cd"] 
[(1..5), (6..10)].map(&:map.with(&:*.with(2)))
# => [[2, 4, 6, 8, 10], [12, 14, 16, 18, 20]]

Here is a conversation I had with @ArupRakshit explaining it further:
Can you supply arguments to the map(&:method) syntax in Ruby?

As @amcaplan suggested in the comment below, you could create a shorter syntax, if you rename the with method to call. In this case, ruby has a built in shortcut for this special method .().

So you could use the above like this:

class Symbol
  def call(*args, &block)
    ->(caller, *rest) { caller.send(self, *rest, *args, &block) }
  end
end

a = [1,3,5,7,9]
a.map(&:+.(2))
# => [3, 5, 7, 9, 11] 

[(1..5), (6..10)].map(&:map.(&:*.(2)))
# => [[2, 4, 6, 8, 10], [12, 14, 16, 18, 20]]

Here is a version using Refinements (which is less hacky than globally monkey patching Symbol):

module AmpWithArguments

  refine Symbol do
    def call(*args, &block)
      ->(caller, *rest) { caller.send(self, *rest, *args, &block) }
    end
  end

end

using AmpWithArguments

a = [1,3,5,7,9]
a.map(&:+.(2))
# => [3, 5, 7, 9, 11] 

[(1..5), (6..10)].map(&:map.(&:*.(2)))
# => [[2, 4, 6, 8, 10], [12, 14, 16, 18, 20]]

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