From: Robert Evans <robert.evans@...>
Date: 2005-11-15T08:07:34+09:00
Subject: Re: removing a constant definition from an environment

Thanks for all responses. I think I can work something out based on  
these. I'll post my answer.

Bob


On Nov 14, 2005, at 2:25 PM, Ryan Leavengood wrote:

> On 11/14/05, Robert Evans <robert.evans@acm.org> wrote:
>> Hi Ryan,
>>
>> Thanks for your help.
>>
>> I tried that, and it didn't work. Here is my irb transcript trying
>> that. Is there another way to remove a constant? I thought I had seen
>> one in the Pickaxe book, but maybe I was thinking of the module  
>> method.
>>
>> irb
>> irb(main):001:0> FOO = "my symbol value"
>> => "my symbol value"
>> irb(main):002:0> remove_const(FOO)
>> NoMethodError: undefined method `remove_const' for main:Object
>>          from (irb):2
>> irb(main):003:0> remove_const(:FOO)
>> NoMethodError: undefined method `remove_const' for main:Object
>>          from (irb):3
>> irb(main):004:0> ??
>>
>>
>> Any other ideas?
>
> This is one of those odd methods that is hard to call. It is actually
> a private method in Module, which means you must call it on a module
> or class, and because it is private you must use send if you want to
> call it from outside the class or module:
>
> irb(main):001:0> FOO = "something"
> => "something"
> irb(main):002:0> Object.const_defined?(:FOO)
> => true
> irb(main):003:0> Object.send(:remove_const, :FOO)
> => "something"
> irb(main):004:0> FOO
> NameError: uninitialized constant FOO
>         from (irb):4
>
> But it is better to do something like this:
>
> irb(main):005:0> class Test
> irb(main):006:1> FOO = "something"
> irb(main):007:1> end
> => "something"
> irb(main):008:0> class Test
> irb(main):009:1> FOO = "something else"
> irb(main):010:1> end
> (irb):9: warning: already initialized constant FOO
> => "something else"
> irb(main):011:0> class Test
> irb(main):012:1> remove_const(:FOO)
> irb(main):013:1> FOO = "yet something else"
> irb(main):014:1> end
> => "yet something else"
>
> In other words you should call remove_const from inside the class
> definition before re-creating it.
>
> Ryan
>