How is each_with_object supposed to work?

Question

I\'m trying to figure out how each_with_object is supposed to be used.

I have a sum example that doesn\'t work:

> (1..3).each_with_ob         


        

Answer 1

The documentation of Enumerable#each_with_object is very clear :

Iterates the given block for each element with an arbitrary object given, and returns the initially given object.

In your case, (1..3).each_with_object(0) {|i,sum| sum+=i},you are passing 0,which is immutable object. Thus here the intial object to each_with_object method is 0,so method returns 0.It works at it is advertised. See below how each_with_object works ,

(1..3).each_with_object(0) do |e,mem|
    p "#{mem} and #{e} before change"
    mem = mem + e
    p mem
end

# >> "0 and 1 before change"
# >> 1
# >> "0 and 2 before change"
# >> 2
# >> "0 and 3 before change"
# >> 3

That means in every pass,mem is set to initial passed object. You might be thinking of the in first pass mem is 0,then in next pass mem is the result of mem+=e,i.e. mem will be 1.But NO,in every pass mem is your initial object,which is 0.