Asp Forum - multiple constructors?

aidy

7/23/2008 5:13:00 PM

Hi,

Is it possible to use multiple constructors in Ruby?

class SQLServerConnection

def initialize(server_name, db)

end

def initialize(server_name, db, user_name, password)

end
end

Thank You

Aidy

5 Answers

Todd Benson

7/23/2008 5:25:00 PM

On Wed, Jul 23, 2008 at 12:09 PM, aidy <aidy.lewis@googlemail.com> wrote:
> Hi,
>
> Is it possible to use multiple constructors in Ruby?
>
> class SQLServerConnection
>
> def initialize(server_name, db)
>
> end
>
> def initialize(server_name, db, user_name, password)
>
> end
> end

You can send your initialize an array or hash, or you can do

class C
def initialize( a, b, *c )
#verify and do stuff
end
end

hth,
Todd

Robert Dober

7/23/2008 5:26:00 PM

On Wed, Jul 23, 2008 at 7:09 PM, aidy <aidy.lewis@googlemail.com> wrote:
> Hi,
>
> Is it possible to use multiple constructors in Ruby?
>
> class SQLServerConnection
>
> def initialize(server_name, db)
>
> end
>
> def initialize(server_name, db, user_name, password)
>
> end
> end
>
> Thank You
>
> Aidy
>
>

First of all initialize is not a constructor but an initializer,
behind the scenes the following happenes

class Object
def self.new *args, &blk
o = allocate
o.send :initialize, *args, &blk # this because #initialize is
*always* private
o
end
end

As you can see #initialize is an instance method and #new is a
singleton (or class) method.

Secondly, and that holds for all methods, #initialize is only an
example, you cannot "overload" method definitions but simulate that
behavior, in your case I would do the following

class SQLServerConnection

private

def initialize *args
case args.size
when 2
init_name_db *args
when 4
init_user_pw *args
else
error
end
end

def init_name_db server_name, db
...
end

def init_user_pwd server_name, db, user, pwd
...
end
end

HTH
Robert

--
http://ruby-smalltalk.blo...

There's no one thing that's true. It's all true.
--
Ernest Hemingway

Rob Biedenharn

7/23/2008 5:26:00 PM

On Jul 23, 2008, at 1:09 PM, aidy wrote:
> Hi,
>
> Is it possible to use multiple constructors in Ruby?
>
> class SQLServerConnection
>
> def initialize(server_name, db)
>
> end
>
> def initialize(server_name, db, user_name, password)
>
> end
> end
>
> Thank You
>
> Aidy

No, but you can have optional parameters by giving a default value or
taking a hash.

def initialize(server_name, db, user_name=nil, password=nil)
if user_name && password
# connect with credentials
else
# connect anonymously
end
end

Called like: SQLServerConnection.new("myserver", "development",
'aidy', 'shh_secret')

-or-

def initialize(server_name, db, options={})
if options.has_key?(:user) && options.has_key?(:password)
# connect with credentials
else
# connect anonymously
end
end

and called like: SQLServerConnection.new("myserver",
"development", :user => 'aidy', :password => 'shh_secret')

-Rob

Rob Biedenharn http://agileconsult...
Rob@AgileConsultingLLC.com

Sebastian Hungerecker

7/23/2008 5:28:00 PM

aidy wrote:
> Is it possible to use multiple constructors in Ruby?

No.

> class SQLServerConnection
> =A0 def initialize(server_name, db)
>
> =A0 end
> =A0 def initialize(server_name, db, user_name, password)
>
> =A0 end
> end

def initialize(server_name, db, user_name=3Dnil, password=3Dnil)

end

HTH,
Sebastian
=2D-=20
Jabber: sepp2k@jabber.org
ICQ: 205544826

Paul Stickney

7/24/2008 8:18:00 PM

I prefer to use different names for "different constructors".
Most of the time, I feel that overloading can complicate things,
more-so in a dynamic language.

Just make them class methods:

Foo.from_x()
Foo.with_size()

Etc, etc.

HTH,
Paul

comp.lang.ruby