Dynamically instantiate a class

ruby-talk
1

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?

2

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?

3

macaco wrote:

type = ['subClass1','subClass2']

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

If you change the first line into

type = [SubClass1, SubClass2] #without quotes

the above works as-is.

HTH,
Sebastian

···

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4

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

···

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!

5

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

···

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!

6

Whoops! This should be:

create_class subClass1

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

--------------------------------------------|
If you're not living on the edge,
then you're just wasting space.

···

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>