[lnkForumImage]
TotalShareware - Download Free Software
Confronta i prezzi di migliaia di prodotti.
Asp Forum
 Home | Login | Register | Search 


 

Forums >

comp.lang.ruby

different methods for initializing one object?

Tool69

12/9/2005 8:54:00 PM

Hi,
let's say I've got a class Point2D to write, it must have 2 methods to
initialize :
1. one with cartesian coordinates i.e : p = Point2D.new(x,y) given the
numbers x and y;
2. a second with polar coordinates i.e : p = Point2D.new(R,theta) given
the radius R>0 and an angle theta;
How can I manage this ?

Thanks.
6 Answers

Mike Fletcher

12/9/2005 9:16:00 PM

0

kibleur.christophe wrote:
> Hi,
> let's say I've got a class Point2D to write, it must have 2 methods to
> initialize :
> 1. one with cartesian coordinates i.e : p = Point2D.new(x,y) given the
> numbers x and y;
> 2. a second with polar coordinates i.e : p = Point2D.new(R,theta) given
> the radius R>0 and an angle theta;
> How can I manage this ?

One way would be to take keyword arguments and figure out which you were
given.

class Point2D
def initialize( params )
if params.has_key? :r and params.has_key? :theta
## initialize from polar
elsif params.has_key? :x and params.has_key? :y
## initialize from cartesian
else
raise ArgumentError.new( "You must provide either :r and :theta OR
:x and :y" )
end
end
end

cart = Point2D.new( :x => 42, :y => -4 )
polar = Point2D.new( :r => 3.14159, :theta => (Math::PI/4) )

--
Posted via http://www.ruby-....

Matthew Desmarais

12/9/2005 9:28:00 PM

0

<snip>

>One way would be to take keyword arguments and figure out which you were
>given.
>
>class Point2D
> def initialize( params )
> if params.has_key? :r and params.has_key? :theta
> ## initialize from polar
> elsif params.has_key? :x and params.has_key? :y
> ## initialize from cartesian
> else
> raise ArgumentError.new( "You must provide either :r and :theta OR
>:x and :y" )
> end
> end
>end
>
>cart = Point2D.new( :x => 42, :y => -4 )
>polar = Point2D.new( :r => 3.14159, :theta => (Math::PI/4) )
>
>
Hi Mike,

What you've proposed is a fine idea, but I think that it's important to
be clear about your terminology. Ruby doesn't currently have keyword
arguments. In the example that you've provided you are passing a hash
with symbols for keys into the initialize method and _not_ using keywords.

Regards,
Matthew J Desmarais

Mike Fletcher

12/9/2005 9:35:00 PM

0

desmarm wrote:
> What you've proposed is a fine idea, but I think that it's important to
> be clear about your terminology. Ruby doesn't currently have keyword
> arguments. In the example that you've provided you are passing a hash
> with symbols for keys into the initialize method and _not_ using
> keywords.

Oop, you're of course correct. It's more "I can't believe it's not
keyword arguments", now with 30% less calories than regular argument
passing (yum, syntactic sugar!).

--
Posted via http://www.ruby-....

Trans

12/9/2005 9:38:00 PM

0

You can also define alternate constructors:

class Point2D

class << self

def new_xy( x, y )
new.set_xy( x, y )
end

def new_rt( r, t )
new.set_rt( r, t )
end

end

def set_xy( x, y )
@x, @y = x, y
end

def set_rt( r, t )
@r, @t = r, t
end

end

p = Point2D.new_xy( x, y )
p = Point2D.new_rt( R, theta )

T.

MenTaLguY

12/9/2005 9:48:00 PM

0

Quoting Mike Fletcher <lemurific+rforum@gmail.com>:

> kibleur.christophe wrote:
> > Hi,
> > let's say I've got a class Point2D to write, it must have 2
> methods to
> > initialize :
> > 1. one with cartesian coordinates i.e : p = Point2D.new(x,y)
> given the
> > numbers x and y;
> > 2. a second with polar coordinates i.e : p =
> Point2D.new(R,theta) given
> > the radius R>0 and an angle theta;
> > How can I manage this ?

If you are always storing cartesian coordinates internally, I'd
suggest introducing a different factory method for creating points
from polar coordinates. For example:

class Point2D
attr_accessor :x, :y

def initialize( x, y )
@x, @y = x, y
end

def self.new_polar( r, theta )
new( r * Math::cos( theta ), r * Math::sin( theta ) )
end
end

examples:

cart = Point2D.new( 42, -4 )
polar = Point2D.new_polar( 3.14159, Math::PI / 4 )

-mental

Tool69

12/9/2005 11:02:00 PM

0

Thanks for all your answers, in fact, my class was already written with
the last mentioned code method.

class Point

attr_accessor :abs, :ord, :name, :cart

def initialize(abs,ord,name="")
@abs = abs
@ord = ord
@name = name
@cart = true
end

def to_s
"#@name : (#{@abs}, #{@ord})"
end

def ==(unPoint)
unPoint.abs = abs and unPoint.ord = ord
end

def Point.new_polaire(rho, theta, name)
@cart = false
@name = name
unPoint = new(rho*cos(theta),rho*sin(theta),@name)
return unPoint
end

end

....but I dislike the calling syntax. I thought it was possible to write
several constructors calls like in Java, ie :

void Move(Vector2D vector) {
center.x += vector.x;
center.y += vector.y;
}

void Move(double x,double y) {
center.x += x;
center.y += y;
}

So, my idea was bad : Ruby is not Java !