ruby - Why does uniq! return nil if there are no duplicates -

i'm starting ruby , find following violation of "principle of least surprise". , is, quoting the documentation, uniq! "removes duplicate elements self. returns nil if no changes made (that is, no duplicates found)."

can explain this, seems counter-intuitive me? means rather being able write 1 line of code below appending .uniq! end first line, instead have write following 2 lines:

  hooks = io.read(wt_hooks_impl_file).scan(/wt_rt_00\w{2}/)   hooks = hooks.uniq 

or missing something, better way?

edit:

i understand uniq! modifies operand. here's problem illustrated better hope:

  hooks = io.read(wt_hooks_impl_file).scan(/wt_rt_00\w{2}/)   puts hooks.length #50   puts hooks.uniq!.length #undefined method `length' nil:nilclass 

i contend way uniq! works makes senseless , useless. sure in case pointed out append .uniq first line. later in same program pushing elements onto array inside of loop. then, under loop, i'd "de-dupe" array, dare not write 'hooks_tested.uniq!' because return nil; instead must write hooks_tested = hooks_tested.uniq

indeed contend particularly egregious mis-feature in known principle that, when devising method returns array, 1 should @ least return empty array, rather nil

this because uniq! modifies self , if uniq! return value wouldn't able know whether change occurred in original object.

var = %w(green green yellow) if var.uniq!   # array contained duplicate entries else   # nothing changed end 

in code can write

hooks = io.read(wt_hooks_impl_file).scan(/wt_rt_00\w{2}/) hooks.uniq! # here hooks changed 

if need return value of hook perhaps because it's last method statement do

def method   hooks = io.read(wt_hooks_impl_file).scan(/wt_rt_00\w{2}/)   hooks.uniq end 

or otherwise

def method   hooks = io.read(wt_hooks_impl_file).scan(/wt_rt_00\w{2}/)   hooks.uniq!   hooks end