Overriding the "for" keyword in Ruby. Is it possible?

Question

I search around and tried overriding the "for" keyword but I found nothing. I am trying something like that:

def for("maybe_arguments_go_here")
  print "Hello from function for!"
end

for i in 1..3
  print "Hello from for"
end

Answer 1

I don't think that 'overriding' a keyword is an option at any language, you can override methods and operators(operators themselves are methods in modern languages) only, for is a keyword in Ruby. However you still can do things like the following:

def loop(range)
  range.each{|i| yield i}
end

loop 1..6 do |x|
  #do something with x
end

Answer 2

If you give the method an explicit receiver it would work, but you would not be able to use the method without explicitly putting self before it.

This would work:

def self.for(arg)
  arg + 1
end

self.for(1)
=> 2

OR

 class Aa
   def c
    self.for(1)
   end

   def for(arg)
     arg + 1
   end
 end

 b = Aa.new
 b.for(4)
 => 5

BUT, I agree with khell and some of the comments above that redefining keywords is a massive no no, of course, if we're just experimenting and having fun, then go for it!

Answer 3

You can't override the keyword itself, but one thing you can do is say what for does for your own classes. for calls each internally, so the following trick will work:

class MyFor
  def initialize(iterable)
    @iterable = iterable
  end

  def each
    @iterable.each do |x|
      puts "hello from for!"
      yield x
    end
  end
end

# convenient constructor
module Kernel
  def my(x)
    MyFor.new(x)
  end
end

for i in my(1..3)
  puts "my for yielded #{x}"
end