Reduce vs each with_object

reduce_with_object.rb

range = (1..10)

range.reduce([]) do |sum, x|
  (sum << x + 2) if x.even? # doesn't work!
end

range.reduce([]) do |sum, x|
  x.even? ? (sum << x + 2) : sum # works...
end

range.each.with_object([]) do |x, sum| 
  (sum << x + 2) if x.even? # works better!
end

# The way reduce works is it sets the 'sum' variable based on the
# return value of the last operation, including the initial value.
# That means each iteration needs to return something so that it
# can be passed along to the next operation.

# Each with object on the other hand does not care about the return 
# value because it is not using it to set the 'sum' variable. Instead 
# 'sum' is set by the initial value and is then passed along in each
# iteration and the final output. That lets you do operations that
# don't return anything, as shown above, making your code more terse.