How do I pass an argument to array.map short cut? [duplicate]

Answer 1

You cannot do it with map. But look at Facets' Enumerable#map_send:

require 'facets'
[1, 2, 3].map_send(:+, 1)
#=> [2, 3, 4]

Writing your own implementation is pretty straightforward:

module Enumerable
  def map_send(*args)
    map { |obj| obj.send(*args) }
  end
end

Answer 2

In this case you can do

a.map(&1.method(:+))

But only because 1 + x is usually the same as x + 1.

Here is a discussion of this practice in a performance context.

Answer 3

You can't do it like this. The & operator is for turning symbols into procs.

a = [1, 2, 3, 4, 5]  
puts a.map(&:to_s) # prints array of strings
puts a.map(&:to_s2) # error, no such method `to_s2`.

& is a shorthand for to_proc:

def to_proc
  proc { |obj, *args| obj.send(self, *args) }
end

It creates and returns new proc. As you see, you can't pass any parameters to this method. You can only call the generated proc.

Answer 4

If you really need that you can use Ampex library, but I don't know if it is still maintained.