Question

I have a Message model that has the following relationships:

belongs_to :sender, Class: "User"
belongs_to :recipient, Class: "User"

I’m attempting to use class_eval to overwrite the recipient method in certain cases.

This works:

def update_recipient(message, recipient_addition = nil)
  message.class_eval <<-EVAL
    def recipient
      "test"
    end
  EVAL
end

message.recipient => “test”

However, this doesn’t:

def update_recipient(message, recipient_addition = nil)
  message.class_eval <<-EVAL
    def recipient
      [#{message.recipient}, #{recipient_addition}]
    end
  EVAL
end

(eval):3: syntax error, unexpected keyword_end, expecting ']'

Answer 1

The first # is misinterpreted as a comment character, discarding the rest of the line. The #{} are expected to be interpolated inside double quotes, though there doesn’t seem to be a reason to put these in #{} right now as they are just simple string values.

["#{message.recipient}", "#{recipient_addition}"]

… unless you’re planning something like:

["To: #{message.recipient}", "CC: #{recipient_addition}"]