Supposed to interesting, concise, clear and useful one-liners

one-liners.rb

# find methods of an Array that have ! equivalents: e.g. map (Note: the method /methods/ returns an Array of /Symbol/s)
[].methods.delete_if{|x| [].methods.index((x.to_s+"!").to_sym) == nil}
#  => [:reverse, :rotate, :sort, :collect, :map, :select, :reject, :slice, :uniq, :compact, :flatten, :shuffle, :sort_by] 
# find methods of a String that have ! equivalents: e.g. sub
"".methods.delete_if{|x| "".methods.index((x.to_s+"!").to_sym) == nil}
#=> [:succ, :next, :upcase, :downcase, :capitalize, :swapcase, :reverse, :sub, :gsub, :chop, :chomp, :strip, :lstrip, :rstrip, :tr, :tr_s, :delete, :squeeze, :slice, :encode]