class Array
def capitalize_words
self.map{|word| word.capitalize!}
end
end
>> ['cde','fgh'].capitalize_words
=> ["Cde", "Fgh"]
>>
但：
>> ['cde','fgh',1,2,3].capitalize_words
NoMethodError: undefined method `capitalize!' for 1:Fixnum
from (irb):3:in `block in capitalize_words'
from (irb):3:in `map'
from (irb):3:in `capitalize_words'
from (irb):8
from /home/www/.rvm/rubies/ruby-2.2.3/bin/irb:11:in `<main>'
>>