Question

In one of my mailer methods I used a variable title ‘@subject’. By default, I was expecting this to be present in the corresponding view. However, after wasting quite some time looking around, I realized that the problem was in the variable name. Changing it to anything but @subject worked. Is there a place where these keywords are defined, I google around but didn’t find any such listing?

Answer 1

Hey @Wahaj first of all @subject is not keyword!, you can use reflection to get information about class before using it.
http://en.wikipedia.org/wiki/Reflection_(computer_programming)#Ruby

You can get all instance method by object_or_class.instance_methods message or just call object.methods will return available methods, there is lots more google it

Now when you call action mailer method like

 UserMailer.welcome(params)

it return Mail::Message object https://github.com/rails/rails/blob/master/actionmailer/lib/action_mailer/base.rb#L143

here is result of Mail::Message reflection

 m=Mail::Message.new => #<Mail::Message:-634435678, Multipart: false, Headers: > 
 m.methods => [....,"subject", "subject=",...]

it seems that subject is attr_accessor in Mail::Message class but it is not, subject getter and setter are setting subject value in a header hash..

#a part from Mail:Message class 
#  mail.subject "G'Day mate"
#  mail.subject #=> "G'Day mate"
def subject( val = nil )
  default :subject, val
end

# Sets the Subject value of the mail object, pass in a string of the field
#
# Example:
#
#  mail.subject = '=?UTF-8?Q?This_is_=E3=81=82_string?='
#  mail.subject #=> "This is あ string"
def subject=( val )
  header[:subject] = val
end