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

Question

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]] 

For your example can be done a.map(&2.method(:+)).

Arup-iMac:$ pry
[1] pry(main)> a = [1,3,5,7,9]
=> [1, 3, 5, 7, 9]
[2] pry(main)> a.map(&2.method(:+))
=> [3, 5, 7, 9, 11]
[3] pry(main)> 

Here is how it works :-

[3] pry(main)> 2.method(:+)
=> #<Method: Fixnum#+>
[4] pry(main)> 2.method(:+).to_proc
=> #<Proc:0x000001030cb990 (lambda)>
[5] pry(main)> 2.method(:+).to_proc.call(1)
=> 3

2.method(:+) gives a Method object. Then &, on 2.method(:+), actually a call #to_proc method, which is making it a Proc object. Then follow What do you call the &: operator in Ruby?.

As the post you linked to confirms, a.map(&:class) is not a shorthand for a.map {|x| x.class} but for a.map(&:class.to_proc).

This means that to_proc is called on whatever follows the & operator.

So you could give it directly a Proc instead:

a.map(&(Proc.new {|x| x+2}))

I know that most probably this defeats the purpose of your question but I can't see any other way around it - it's not that you specify which method to be called, you just pass it something that responds to to_proc.

There is another native option for enumerables which is pretty only for two arguments in my opinion. the class Enumerable has the method with_object which then returns another Enumerable.

So you can call the & operator for a method with each item and the object as arguments.

Example:

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

In the case you want more arguments you should repeat the proccess but it's ugly in my opinion:

a = [1,3,5,7,9]
a.to_enum.with_object(2).map(&:+).to_enum.with_object(5).map(&:+) # => [8, 10, 12, 14, 16]

Short answer: No.

Following @rkon's answer, you could also do this:

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