Ruby - Why use "until" when "while" can do the same [closed]

Question

This is the code using while:

i = 0
num = 5

while i < num do
   puts "Inside the loop! i = #{i}"
   i += 1
end

This is the code using until:

i = 0
num = 5

until i > num do
   puts "Inside the loop! i = #{i}"
   i += 1
end

Can someone give an example of when one should be preferred instead of the other? For me, there is no reason to have until and while if they do the same thing. In my opinion, this is the reason why other programming languages don't have both.

Answer 1

Which is better:

1. makeSoup while !ingredients.empty?
2. makeSoup until ingredients.empty?

while and until do the same thing, one is just "nicer" to read in some instances.

Answer 2

It's about readability. A "correct" example is completely subjective:

done = my_function until done

or

done = false
until done
 # better than "while not done"? Who can say?
 # do something that modifies the state of done
end

or

my_object.do_something until my_object.complete
# Or, if the method were otherwise named...
my_object.do_something while my_object.incomplete