正常的方法调用

class A
  def self.f1
    puts "the method of class"
  end
  def f2
    puts "the method of instance"
  end
end

A.f1
A.new.f2

UserMailer 的方法调用

class UserMailer < ApplicationMailer
  def account_activation(user)
    @user = user
    mail(to: @user.email, subject: '激活帐号.')
  end
end

UserMailer.account_activation(@user).deliver_now

不应该是这样调用么？

UserMailer.new.account_activation(@user).deliver_now