By jriff

2011-01-15 12:57:21 8 Comments

This is not specific for Rails - I am just using Rails as an example.

I have a model in Rails:

class Item < ActiveRecord::Base

  def hello
    puts "Hello, #{}"

(Let's say that the Item model (class) has a method called name). When do I need to use and when can I just use name? (Eg. #{name})


@Phrogz 2011-01-15 18:30:58

  1. It is idiomatic to prefer to omit self. when invoking methods; it is generally never needed.

  2. You must use = xxx when calling a setter method, instead of foo = xxx, so that Ruby realizes that you are not trying create a new local variable.

    • Similarly, in the unlikely event that you have an existing local variable do_something with the same name as a method, you must use self.do_something to invoke the method, as just do_something will end up reading the variable.
  3. You cannot use to call a private method; you must instead call just foo(...).

@tokland 2011-01-15 13:05:32

If you omit self Ruby will first look for local variables with that name, then for an instance method. It's not idiomatic to write self.. In any case, you have to write self.something = value on assignations.

Note that you cannot use self when calling private methods (no problem with protected methods):

class A
  def foo;; end


  def bar; "bar"; end
# private method `bar' called for #<A:0x7f49193584f0> (NoMethodError)

@shybovycha 2011-01-15 13:04:48

Following this tutorial, you have no need to use self pointer. But i think this (or self in our case) pointers are used to resolve name conflicts. Actually, @name and are the same statements (if there is no name method for your class). E.g.:

class Moo
  attr_accessor :name

  def moo(name)
    name = name # O_o which *name* should i use?

  def foo(name)
    @name = name # the same as * = name*

  def hello
    puts # the same as *puts @name*

a =
a.hello() # should give no output

a.hello() # Hey! Why does it prints nothing?'zaooza')
a.hello() # whoa! This one shows 'zaooza'!

Try running this code and you'll see =)

@Marcel Jackwerth 2011-01-15 13:14:50

Also a special case: methods named foo= MUST be called via, otherwise it defines a new variable named foo.

@shybovycha 2011-01-15 13:17:51

Yeah, you're right. Sorry, i've overlooked that and totally forgot about operators...

@sepp2k 2011-01-15 15:31:20

@name and are definitely not the same statement. is a method call and @name is an instance variable. It's just that in your example (but not in the OP's), is a method which happens to return @name. In the OP's example will get the value stored in the database and @name will simply be nil, so they're definitely not the same.

@sepp2k 2011-01-15 18:35:28

@shybovycha: Nope, that's not corrected. If there is no name method, will cause a NoMethodError. is always a method call. It is never a variable (though it might very well return the contents of a variable).

@Matt Briggs 2011-01-15 18:42:22

sepp is right. also idiomatically, I don't think I have ever seen anyone use empty parens on a method call before in ruby.

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