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comp.lang.ruby

Dynamically instantiate a class

macaco

2/7/2008 2:14:00 AM

[Note: parts of this message were removed to make it a legal post.]

Hi.

I've been wondering if I can instantiate during execution, I have this
subclasses, but I don't know how to do it by their name as a string.

This is what I mean:

class superClass
...
end

class subClass1 < superClass
...
end

class subClass2 <superClass
...
end

class caller
type = ['subClass1','subClass2']

def create_class(var)
#instantiate class type[var]
newClass = type[var].new # ?????
end
end

I don't wanna do it with a case clause, cos I don't know when I'm going to
add more subclasses.

Any idea?
5 Answers

macaco

2/7/2008 2:32:00 AM

0

[Note: parts of this message were removed to make it a legal post.]

I've found this:

def create_class(var)
#instantiate class type[var]
foo = Object.const_get(type[var])
sub = foo.new
puts "#{sub.class}"
end

Works for me!

On 2/6/08, macaco <macacoangel@gmail.com> wrote:
>
> Hi.
>
> I've been wondering if I can instantiate during execution, I have this
> subclasses, but I don't know how to do it by their name as a string.
>
> This is what I mean:
>
> class superClass
> ...
> end
>
> class subClass1 < superClass
> ...
> end
>
> class subClass2 <superClass
> ...
> end
>
> class caller
> type = ['subClass1','subClass2']
>
> def create_class(var)
> #instantiate class type[var]
> newClass = type[var].new # ?????
> end
> end
>
> I don't wanna do it with a case clause, cos I don't know when I'm going to
> add more subclasses.
>
> Any idea?
>

Day

2/7/2008 4:13:00 AM

0

On Feb 6, 2008 8:32 PM, macaco <macacoangel@gmail.com> wrote:
> I've found this:
>
> def create_class(var)
> #instantiate class type[var]
> foo = Object.const_get(type[var])
> sub = foo.new
> puts "#{sub.class}"
> end
>
> Works for me!
So you're not creating a class, really. You're creating an instance of
already-defined classes. Right?

You can smash those down to one line and get rid of your holder
variable, if you like:

def create_thing var
sub = Object.const_get(type[var]).new
puts sub.class
end

I'm not a huge fan of holder variables, myself, but your mileage may
vary, of course.


Ben

Sebastian Hungerecker

2/7/2008 6:37:00 AM

0

macaco wrote:
> =A0 =A0type =3D ['subClass1','subClass2']
>
> =A0 def create_class(var)
> =A0 =A0 #instantiate class type[var]
> =A0 =A0 newClass =3D type[var].new # ?????
> =A0 end

If you change the first line into

type =3D [SubClass1, SubClass2] #without quotes

the above works as-is.

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

fedzor

2/7/2008 3:22:00 PM

0


On Feb 6, 2008, at 9:32 PM, macaco wrote:

> I've found this:
>
> def create_class(var)
> #instantiate class type[var]
> foo = Object.const_get(type[var])
> sub = foo.new
> puts "#{sub.class}"
> end
>
> Works for me!

Or you could do this:

def create_class klass
klass.new
end

create_class "subClass1" #=> #<subClass1>

BTW, can you have a class name that's NOT a constant?

-------------------------------------------------------|
~ Ari
if god gives you lemons
YOU FIND A NEW GOD

fedzor

2/7/2008 11:18:00 PM

0


On Feb 7, 2008, at 10:22 AM, fedzor wrote:

> Or you could do this:
>
> def create_class klass
> klass.new
> end
>
> create_class "subClass1" #=> #<subClass1>

Whoops! This should be:

create_class subClass1

when you create a class, it assigns the class to the name you give it

--------------------------------------------|
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then you're just wasting space.