How to access variables from within class definition

Ruby
1

I’ve got something like:

@var = ‘brown’

class Foo < ActiveRecord::Base
set_table_name @var
end

However, as the code is right now, I’m not able to access @var from
within the class definition. Can someone tell me how I can accomplish
this?

2

Maybe you want to use global instead instance variable here:

I’ve got something like:

@var = ‘brown’
$var = ‘brown’

class Foo < ActiveRecord::Base
set_table_name @var
set_table_name $var

-Jan

3

eggman2001 wrote:

I’ve got something like:

@var = ‘brown’

class Foo < ActiveRecord::Base
set_table_name @var
end

However, as the code is right now, I’m not able to access @var from
within the class definition. Can someone tell me how I can accomplish
this?

Of course you can’t see @var from within the class definition if you set
it outside. Remember that @variables are instance variables, and are
scoped to the class definition.

If you can explain where you’re trying to set @var, perhaps we can come
up with an alternative approach.

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

4

eggman2001 wrote:

I’ve got something like:

@var = ‘brown’

This is an instance variable of the top-level (main) object.

class Foo < ActiveRecord::Base
set_table_name @var
end

Now you’re inside class Foo, @var is an instance variable of the Foo
class object (sometimes called a “class instance variable”, but it’s
just an instance variable like any other)

However, as the code is right now, I’m not able to access @var from
within the class definition. Can someone tell me how I can accomplish
this?

(1) Horrible:

class Foo < ActiveRecord::Base
set_table_name eval("@var", TOPLEVEL_BINDING)
end

(2) Much better to use a local variable:

var = ‘brown’
Foo.set_table_name var

That should work unless set_table_name is a private method. If it is,
then:

(3)
var = ‘brown’
Foo.class_eval { set_table_name var }

You see that local variables propagate happily into blocks. It’s only
‘class’ and ‘def’ which start with a clean slate as far as local
variables are concerned.

5

2009/5/27 eggman2001 [email protected]:

this?

You can do it using eval like this:

@var = ‘brown’
class Foo
p eval(‘@var’,TOPLEVEL_BINDING)
end

Regards,
Park H.

6

This helps a lot. Guess I should brush up on my variable types :slight_smile: