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comp.lang.ruby

Adding methods to String, but only in my own Module?

Greg Hurrell

1/25/2007 9:34:00 PM

Is there any way to add methods to the String class, but only within
the scope of a particular module? Example: adding a "fantastic" method
to String:

class String
def fantastic
self + "fantastic"
end
end

Now, given the limited usefulness of the "fantastic" method, I'd like
to be able to confine its impact to my Module only:

# outside of my module this should raise a NoMethodError
"foo".fantastic

class Example
def example
"foo".fantastic # should work
end
end

I suspect the answer is going to be no, but wanted to ask anyway...

Cheers,
Greg
4 Answers

Jos Backus

1/25/2007 9:50:00 PM

0

On Fri, Jan 26, 2007 at 06:35:07AM +0900, Greg Hurrell wrote:
> Is there any way to add methods to the String class, but only within
> the scope of a particular module?

Glad to see I'm not the only one interested in this. See Pit Capitain's
solution in the thread at

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby...

While I'm grateful for Pit's suggestion it's a rather suboptimal solution to
the problem imho, and I wish this were possible in Ruby in a straightforward
manner somehow.

--
Jos Backus
jos at catnook.com

Gary Wright

1/25/2007 11:57:00 PM

0


On Jan 25, 2007, at 4:50 PM, Jos Backus wrote:
> On Fri, Jan 26, 2007 at 06:35:07AM +0900, Greg Hurrell wrote:
>> Is there any way to add methods to the String class, but only within
>> the scope of a particular module?
>
> Glad to see I'm not the only one interested in this. See Pit
> Capitain's
> solution in the thread at
>
> http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby...
>
> While I'm grateful for Pit's suggestion it's a rather suboptimal
> solution to
> the problem imho, and I wish this were possible in Ruby in a
> straightforward
> manner somehow.

ruby-core: this was originally just a response to Jos, but it has some
thoughts related to the public/protected/private discussion on ruby-core

The problem with the import-module solution is that it is ultimately
manipulating a global data structure (the class/module hierarchy) so
that the visibility of the changes (even if temporary) is defined
temporally and globally rather then lexically localized to particular
modules or classes.

One of the interesting aspects of Plan 9 is the idea of per-process
namespaces. In Plan 9, the file system is not a global data structure
that is visible to and shared by all processes. Instead, each
process constructs its own private view of the world. There are various
mechanisms to allow processes to share views (default) or to create
and manipulate their own private hierarchy (think of per-process
symlinks).

Switching back to Ruby, I wonder if the Plan 9 concepts of private
file hierarchies could be adapted to permit per-module/class views of
the
class hierarchy?

class A
enhance String, MyModule
def foo
"bar".my_method # my_method is resolved to MyModule#mymethod
# because the enhancement is visible in
A#foo
B.new.baz
end
end

class B
def baz
"bar".my_method # NameError because the enhancement is not
# visible in B.
end
end

The idea is that when methods *defined* in A are executing, they
see the String class enhanced (i.e. included) via MyModule. Methods
that are not explicitly defined within A don't see the enhancements.

I feel like this sort of thing is related to the ongoing discussion of
private over on ruby-core where the goal is to figure out how to keep
private methods visible only in a particular lexical scope (at least I
think that is the/a goal).

How about:

class A
enhance self do
def private_method_1
end
end

def public_method
private_method_1
end
end

A.new.private_method_1 # NameError

My main point is that as long as the class-hierarchy is considered a
global
data structure you are going to have a hard time dealing with name
clashes.
Having a way to construct lexically scoped class-hierarchies may be a
way around
this problem.

Gary Wright

Jos Backus

1/26/2007 4:35:00 AM

0

On Fri, Jan 26, 2007 at 08:57:11AM +0900, gwtmp01@mac.com wrote:
[snip]
> My main point is that as long as the class-hierarchy is considered a global
> data structure you are going to have a hard time dealing with name clashes.
> Having a way to construct lexically scoped class-hierarchies may be a way
> around this problem.

Well put, thank you Gary.

--
Jos Backus
jos at catnook.com

Robert Klemme

1/26/2007 8:20:00 AM

0

On 25.01.2007 22:34, Greg Hurrell wrote:
> Is there any way to add methods to the String class, but only within
> the scope of a particular module? Example: adding a "fantastic" method
> to String:
>
> class String
> def fantastic
> self + "fantastic"
> end
> end
>
> Now, given the limited usefulness of the "fantastic" method, I'd like
> to be able to confine its impact to my Module only:
>
> # outside of my module this should raise a NoMethodError
> "foo".fantastic
>
> class Example
> def example
> "foo".fantastic # should work
> end
> end
>
> I suspect the answer is going to be no, but wanted to ask anyway...

See the other replies for suggested solutions etc. For me it always
seemed easier to use /functions/ for this:

def fantastic(s)
s + "fantastic"
end

And you can scope them as you like / need.

Kind regards

robert