From: Mark Cox <mark_cox@...>
Date: 2003-12-10T11:22:05+09:00
Subject: Re: Adjusting the Scope of Blocks

Thanks for your reply.

I've written a ruby binding for the low level terminal IO functions
for unix. There is about 60 to 80 constants so I was sort of hoping to 
remove the need to do Foo::Const all the time to set flags.

I know I'm just lazy. :)

Mark.

Robert Klemme wrote:

> 
> "Gavin Sinclair" <gsinclair@soyabean.com.au> schrieb im Newsbeitrag
> news:49755.203.185.214.34.1070949030.squirrel@webmail.imagineis.com...
>> > Hi,
>> >
>> > Is there a way to give a block associated with a method call the same
>> > scope  as if it were executing inside the method.
>> >
>> > ie.
>> >
>> > class Foo
>> >    ACONST = 1
>> >
>> >    def input_flags
>> >         @FLAG_SEL = INPUT
>> >         yield
>> >    end
>> >
>> >    def output_flags
>> >         @FLAG_SEL = OUTPUT
>> >         yield
>> >    end
>> >
>> >    def set(flgs)
>> >         set_flags(@FLAG_SEL, flgs)
>> >    end
>> > end
>> >
>> > f = Foo.new
>> >
>> > f.input_flags {
>> >   set ACONST
>> > }
>> >
>> > f.output_flags {
>> >   set ACONST
>> > }
>>
>>
>> I've never done it myself, but you might try:
> 
> This works as expected.  Note however that with this approach method local
> variables are not accessible.
> 
>>   class Foo
>>     def input_flags(&block)
>>       @FLAG_SEL = INPUT
>>       instance_eval &block
>>     end
>>   end
> 
> You can of course yield all values that should be accessible for the
> block.
> 
> Another approach is to use "eval" with a binding, although be warned that
> this can have serious security implications:
> 
> def tester(code)
>   foo="bar"
>   b = binding
>   eval( code, b )
> end
> 
> tester "puts foo"
> => prints "bar"
> 
> But why don't you just make "input_flags" and "output_flags" accessors to
> member variables?  Then you can do "foo.input_flags |= Foo::ACONST".
> 
> Or you define a special bit set type:
> 
> class Bitset
>   attr_accessor :val
>   def initialize(v=0); @val=0; end
> 
>   def set(x); @val|=x; end
>   def toggle(x); @val^=x; end
>   def reset(x); set(x); toggle(x); end
>   def to_i; val; end
> end
> 
> Kind regards
> 
>     robert