Confused about method definition: def req=(request)

Question

I found this in Ryan Bates' railscast site, but not sure how it works.

#models/comment.rb
def req=(request)
    self.user_ip    = request.remote_ip
    self.user_agent = request.env['HTTP_USER_AGENT']
    self.referrer   = request.env['HTTP_REFERER']
end

#blogs_controller.rb
def create
    @blog = Blog.new(params[:blog])
    @blog.req = request
    if @blog.save
        ...

I see he is saving the user ip, user agent and referrer, but am confused with the req=(request) line.

Answer 1

To build on Karmen Blake's answer and KandadaBoggu's answer, the first method definition makes it so when this line is executed:

@blog.req = request

It's like doing this instead:

@blog.user_ip    = request.remote_ip
@blog.user_agent = request.env['HTTP_USER_AGENT']
@blog.referrer   = request.env['HTTP_REFERER']

It basically sets up a shortcut. It looks like you're just assigning a variable's value, but you're actually calling a method named req=, and the request object is the first (and only) parameter.

This works because, in Ruby, functions can be used with or without parentheses.

Answer 2

That line defines a method called req=. The = character in the end makes it an assignment method.

This is a regular setter method:

def foo(para1)
  @foo = para1
end

The setter method can be re-written as an assignment method as follows:

def foo=(para1)
  @foo = para1
end

Difference between the two setter methods is in the invocation syntax.

Assignment setter:

a.foo=("bar")   #valid syntax
a.foo= ("bar")  #valid syntax
a.foo = ("bar") #valid syntax
a.foo= "bar"    #valid syntax
a.foo = "bar"   #valid syntax

Regular setter:

a.foo("bar")    #valid syntax
a.foo ("bar")   #valid syntax
a.fo o ("bar")  #invalid syntax