title: Rails - Pass variable in flash notice
body: <p>I've been trying to add a variable in the flash notice that appears when post been created with <code>#{variable}</code></p>
  
  <p>But I must be missing something because the only message I receive is "#{variable}".</p>
  
  <p>This is my controller:</p>
  
  <pre><code> def create
  
      @participant = Participant.new(params[:participant])
  
      respond_to do |format|
        if @participant.save
          mail = params[:email]
          format.html { redirect_to @participant, notice: 'Thanks, We will be sending out instructions to:  #{mail}' }
          format.json { render json: @participant, status: :created, location: @participant }
        else
          format.html { render action: "new" }
          format.json { render json: @participant.errors, status: :unprocessable_entity }
        end
      end
    end
  </code></pre>
  
  <p>I've been trying with @participants as variable aswell, but still, I don't get anything but the actual "#{@participants}" in the message.</p>