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comp.lang.ruby

Using Fixnum, Strings etc. in Modules

Bram Wijnands

3/18/2009 1:11:00 PM

I'm stuck on why this occurs. (using jRuby 1.1.5 & Ruby 1.8.6)

I'm trying to use modules to scope certain class overrides, so say the
String class is changed in ModuleA i don't want it to affect ModuleB.
But when i try to accomplish this i run in to two things.

First, when creating a Module and overwriting, just for example, the
reverse method. results in an error:
module ModuleA
class String; def reverse;false;end; end
p String.new("abc").reverse
end

Okay, so it creates its own class String instead of taking the core
class String. Basicly what i want is the module to have it's own set of
core classes.

Secondly, when using direct instantiation in a module it wont use the
overwritten class, example:
module ModuleA
class String < String; def reverse;false;end; end
p String.new("abc").reverse
p "abc".reverse
end

Results in:
false
cba
Instead of false; false

Could anyone point me in the right drection, thanks in advanced !
--
Posted via http://www.ruby-....
3 Answers

A to Z

3/16/2009 11:39:00 PM

0


"FerretBill" <Winky65@comcast.net> wrote in message
news:1qmtr49o6rro3vbehq9g43qb1k8fq81v83@4ax.com...
> On Mon, 16 Mar 2009 18:00:21 -0400, "A to Z"
> <REMOVETHESEaddietzCAPS@verizonPLEASE.net> wrote:
>
>>
>>"spoonful2" <spoonful2@gmail.com> wrote in message
>>news:894578a3-ae15-4ca7-96c4-e16de3172b15@j39g2000yqn.googlegroups.com...
>>>A pure copy/paste from BTX:
>>>
>>> According to Pac401: No Bruce, no Clarence, and no Steve. Nils on
>>> vocals
>>> 15) Bobby Jean
>>
>>oh, thank God, I was worried they might forget that one
>>
>>
>>
> Bitching already? How will you feel when they work on Lonesome Day
> multiple times tomorrow?

very much gladder
for a small bladder


Christopher Dicely

3/18/2009 2:51:00 PM

0

On Wed, Mar 18, 2009 at 6:10 AM, Bram Wijnands <brambomail@gmail.com> wrote=
:
> I'm stuck on why this occurs. (using jRuby 1.1.5 & Ruby 1.8.6)
>
> I'm trying to use modules to scope certain class overrides, so say the
> String class is changed in ModuleA i don't want it to affect ModuleB.
> But when i try to accomplish this i run in to two things.
>
> First, when creating a Module and overwriting, just for example, the
> reverse method. results in an error:
> module ModuleA
> class String; def reverse;false;end; end
> =C2=A0p String.new("abc").reverse
> end
>
> Okay, so it creates its own class String instead of taking the core
> class String. Basicly what i want is the module to have it's own set of
> core classes.
>
> Secondly, when using direct instantiation in a module it wont use the
> overwritten class, example:
> module ModuleA
> class String < String; def reverse;false;end; end
> p String.new("abc").reverse
> p "abc".reverse
> end
>
> Results in:
> false
> cba
> Instead of false; false
>
> Could anyone point me in the right drection, thanks in advanced !

I don't think its possible to do exactly what you are trying to do
without fundamentally altering the core of Ruby: you can't, as far as
I know, alter a class only for purposes of calls from a particular
module, and literals will always use the top level class (::String,
etc.) not <CurrentModule>::String. As your code above shows, you can
just avoid using literals and always use explicit constructor calls in
your module to use the local version.

Robert Klemme

3/18/2009 3:29:00 PM

0

2009/3/18 Christopher Dicely <cmdicely@gmail.com>:
> On Wed, Mar 18, 2009 at 6:10 AM, Bram Wijnands <brambomail@gmail.com> wro=
te:
>> I'm stuck on why this occurs. (using jRuby 1.1.5 & Ruby 1.8.6)
>>
>> I'm trying to use modules to scope certain class overrides, so say the
>> String class is changed in ModuleA i don't want it to affect ModuleB.
>> But when i try to accomplish this i run in to two things.
>>
>> First, when creating a Module and overwriting, just for example, the
>> reverse method. results in an error:
>> module ModuleA
>> class String; def reverse;false;end; end
>> =A0p String.new("abc").reverse
>> end
>>
>> Okay, so it creates its own class String instead of taking the core
>> class String. Basicly what i want is the module to have it's own set of
>> core classes.
>>
>> Secondly, when using direct instantiation in a module it wont use the
>> overwritten class, example:
>> module ModuleA
>> class String < String; def reverse;false;end; end
>> p String.new("abc").reverse
>> p "abc".reverse
>> end
>>
>> Results in:
>> false
>> cba
>> Instead of false; false
>>
>> Could anyone point me in the right drection, thanks in advanced !
>
> I don't think its possible to do exactly what you are trying to do
> without fundamentally altering the core of Ruby: you can't, as far as
> I know, alter a class only for purposes of calls from a particular
> module, and literals will always use the =A0top level class (::String,
> etc.) not <CurrentModule>::String. As your code above shows, you can
> just avoid using literals and always use explicit constructor calls in
> your module to use the local version.

Absolutely agree! Fiddling with core classes is a bad idea(TM).

And you cannot alter the return type of String constructors "" and ''.

Another solution is to use a functional approach

module A
def self.reverse(str)
false
end
end

You could as well use delegation to wrap core classes with other
classes and add / change functionality. That's probably the most OO
approach. Changing core classes brings all sorts of problems and I
strongly suggest to not do it.

Cheers

robert

--=20
remember.guy do |as, often| as.you_can - without end