Question

Possible Duplicate:
Shorter way to pass every element of an array to a function

I know this will work:

def inc(a)
  a+1
end
[1,2,3].map{|a| inc a}

but in Python, I just need to write:

map(inc, [1,2,3])

or

[inc(x) for x in [1,2,3])

I was wondering whether I can skip the steps of making a block in Ruby, and did this:

[1,2,3].map inc
# => ArgumentError: wrong number of arguments (0 for 1)
# from (irb):19:in `inc'

Does anyone have ideas about how to do this?

Answer 1

According to “Passing Methods like Blocks in Ruby“, you can pass a method as a block like so:

p [1,2,3].map(&method(:inc))

Don’t know if that’s much better than rolling your own block, honestly.

If your method is defined on the class of the objects you’re using, you could do this:

# Adding inc to the Integer class in order to relate to the original post.
class Integer
  def inc
    self + 1
  end
end

p [1,2,3].map(&:inc)

In that case, Ruby will interpret the symbol as an instance method name and attempt to call the method on that object.

---

The reason you can pass a function name as a first-class object in Python, but not in Ruby, is because Ruby allows you to call a method with zero arguments without parentheses. Python’s grammar, since it requires the parentheses, prevents any possible ambiguity between passing in a function name and calling a function with no arguments.