Where and when to use Lambda?

Question

I am trying to understand why do we really need lambda or proc in ruby (or any other language for that matter)?

#method
def add a,b
  c = a+b
end

#using proc
de         


        

Answer 1

I found this helpful in understanding the differences:

http://www.robertsosinski.com/2008/12/21/understanding-ruby-blocks-procs-and-lambdas/

But in general the point is sometimes your writing a method but you don't know what you're going to want to do at a certain point in that method, so you let the caller decide.

E.g.:

def iterate_over_two_arrays(arr1, arr2, the_proc)
  arr1.each do |x|
    arr2.each do |y|
      # ok I'm iterating over two arrays, but I could do lots of useful things now
      #  so I'll leave it up to the caller to decide by passing in a proc
      the_proc.call(x,y)
    end
  end
end

Then instead of writing a iterate_over_two_arrays_and_print_sum method and a iterate_over_two_arrays_and_print_product method you just call:

iterate_over_two_arrays([1,2,3], [4,5,6], Proc.new {|x,y| puts x + y }

or

iterate_over_two_arrays([1,2,3], [4,5,6], Proc.new {|x,y| puts x * y }

so it's more flexible.