when '=' can be used just after 'if' in Ruby/Rails? -

i have noticed metod, while looking through activemodel::serializable

def as_json(args={})   if root = args[:root] || options[:root]     options[:hash] = hash = {}     options[:unique_values] = {}      hash.merge!(root => serialize)     include_meta hash     hash   else     serialize   end end 

and dont know how 'if root =' works... shouldn't 'if root =='?

if root = args[:root] || options[:root] 

this assign value of args[:root] root if args[:root] not nil. if nil, assign options[:root] root. if final result of root not nil, first branch of if taken. if nil, else branch taken.