Freeze not freezing

[Ralph Shnelvar]

Note that I am new to this list and to Ruby.


Consider ...

irb(main):020:0> c=[0,1]
=> [0, 1]
irb(main):021:0> c[0].freeze
=> 0
irb(main):022:0> c[0]=2
=> 2
irb(main):023:0> c
=> [2, 1]
irb(main):024:0>


Similarly ...


irb(main):029:0> f=1
=> 1
irb(main):030:0> f.freeze
=> 1
irb(main):031:0> f=2
=> 2




It took a few moments for me to scratch my head and then I thought
that the reason that there was no message when c[0] or f changed was that
c[0] is not an object but a reference to an object (the number 2).

So I searched the archives and it appears taht my reasoning is
correct.  I think.

there was the suggestion to make f a constant, F.  Yes, that generates
a warning ... but it is not what I want.  I want to freeze the
reference as well as the object.

In C++ it is possible to "freeze" (i.e. const) both a pointer to an
object and the object itself.  Is this possible in Ruby?


a) Is my reasoning correct?

b) Is there a way to do what I want? That is, freeze f or c[0] so that
I get some sort of message/error/exception?

c) Do my examples violate POLS?

[Yukihiro Matsumoto]

Hi,

In message "Re: Freeze not freezing"
    on Thu, 5 Nov 2009 23:05:28 +0900, Ralph Shnelvar <ralphs@...> writes:

|a) Is my reasoning correct?

#freeze protect an object from modification.  The reference is not the
target of freezing.

|b) Is there a way to do what I want? That is, freeze f or c[0] so that
|I get some sort of message/error/exception?

You can protect an array (or object) as a whole, since it is an
object, so that

  c=[0,1]
  c.freeze
  c[0]=2    # => can't modify frozen array (RuntimeError)

but you cannot freeze any variables.

|c) Do my examples violate POLS?

No.  Unlike C++, variables and references are not object in any sense
in Ruby.  From my viewpoint, C++ violates POLS. ;-)

                                                        matz.

[Ralph Shnelvar]

Matz,

I deeply appreciate your answer.

But I will repeat part of the question: Is there a way to detect ...
in the general case ... that the reference to an object has changed?

In a more C-like environment, a debugger is able to detect (via
hardware) that a location in memory has changed.  Is something similar
available in Ruby?

Where is the Ruby debugger (watch, etc.) documented?

Ralph


Thursday, November 5, 2009, 7:14:11 AM, you wrote:

YM> Hi,

YM> In message "Re: Freeze not freezing"
YM>     on Thu, 5 Nov 2009 23:05:28 +0900, Ralph Shnelvar <ralphs@...> writes:

YM> |a) Is my reasoning correct?

YM> #freeze protect an object from modification.  The reference is not the
YM> target of freezing.

YM> |b) Is there a way to do what I want? That is, freeze f or c[0] so that
YM> |I get some sort of message/error/exception?

YM> You can protect an array (or object) as a whole, since it is an
YM> object, so that

YM>   c=[0,1]
YM>   c.freeze
YM>   c[0]=2    # => can't modify frozen array (RuntimeError)

YM> but you cannot freeze any variables.

YM> |c) Do my examples violate POLS?

YM> No.  Unlike C++, variables and references are not object in any sense
YM> in Ruby.  From my viewpoint, C++ violates POLS. ;-)

YM>                                                         matz.




--
Best regards,
 Ralph                            mailto:ralphs@...

[Jordi Bunster]

[Seebs-3]

On 2009-11-05, Yukihiro Matsumoto <matz@...> wrote:
> From my viewpoint, C++ violates POLS. ;-)

Sturgeon's Law:  90% of everything is crud.

If you know this, C++ does not violate POLS.  :)

-s
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