I am working my way through some tutorials and books on Ruby and i am
trying to understand the various uses of the self object. For example
this code from Agile rails:
def self.login(name,password)
code here
end
def try_to_login
User.login(self.name, self.password)
end
#Both functions belong to a class Named User
Now I understand the self.name and self password reference the calling
object. However, I am still trying to figure out why in this example the
function is prefixed with self.
Ben
On 5/5/06, Benjamin P. [email protected] wrote:
Now I understand the self.name and self password reference the calling
object. However, I am still trying to figure out why in this example the
function is prefixed with self.
In your example, declaring “login” as “self.login” means it’s a class
method (similar to a static method in Java). It belongs to the User
class, rather than to a specific instance or User, which means you
don’t need to instantiate a new User object in order to use it.
On May 5, 2006, at 2:51 PM, Benjamin P. wrote:
I am working my way through some tutorials and books on Ruby and i am
trying to understand the various uses of the self object. For example
this code from Agile rails:
def self.login(name,password)
code here
end
Here, self refers to the class
class NamedUser
inside here, self = NamedUser
we are defining a method that can be called like NamedUser.login or
NamedUser::login
def self.login(…)
…
end
def try_to_login(…)
# inside here self will be an instance of NamedUser instead of
# NamedUser itself
end
end
You should probably google singleton classes to really understand
what’s going on
On May 05, 2006, at 7:51 pm, Benjamin P. wrote:
Now I understand the self.name and self password reference the calling
object. However, I am still trying to figure out why in this
example the
function is prefixed with self.
If by “the function” you mean “def self.login” it’s to make it a
class method, rather than a method that applies to objects of that
class. ie you call “User.login” and not “u = User.new; u.login”.
Ashley
Bira wrote:
On 5/5/06, Benjamin P. [email protected] wrote:
Now I understand the self.name and self password reference the calling
object. However, I am still trying to figure out why in this example the
function is prefixed with self.
In your example, declaring “login” as “self.login” means it’s a class
method (similar to a static method in Java). It belongs to the User
class, rather than to a specific instance or User, which means you
don’t need to instantiate a new User object in order to use it.
Thanks for the clarification, it really helps clear things up.
Ben
Ashley M. wrote:
On May 05, 2006, at 7:51 pm, Benjamin P. wrote:
Now I understand the self.name and self password reference the calling
object. However, I am still trying to figure out why in this
example the
function is prefixed with self.
If by “the function” you mean “def self.login” it’s to make it a
class method, rather than a method that applies to objects of that
class. ie you call “User.login” and not “u = User.new; u.login”.
Ashley
Thank you for supplying a example, It makes things even more clear then
the other definitions provided here.
Ben
On Friday 05 May 2006 12:51 pm, Benjamin P. wrote:
def self.login(name,password)
code here
end
def try_to_login
User.login(self.name, self.password)
end
Now I understand the self.name and self password reference the calling
object. However, I am still trying to figure out why in this example the
function is prefixed with self.
Keep in mind the context that the code is executing in:
class Foo
def Foo.bar {“bar here”}
def self.qux {“qux here”}
end
Foo.bar is clear. It is declaring the method to be a class method of
Foo.
self.qux is doing the same thing. It is declaring qux to be a class
method of
whatever self is. Remember that classes are themselves objects. That
object
is what self contains in that instance.
Maybe this helps you see how it works?
irb(main):001:0> class Foo
irb(main):002:1> puts self.object_id
irb(main):003:1> end
359445590
=> nil
irb(main):004:0> a = Foo
=> Foo
irb(main):005:0> puts a.object_id
359445590
=> nil
irb(main):006:0> def a.qux; 7; end
=> nil
irb(main):007:0> puts Foo.qux
7
Kirk H.