[Pharo-users] how to test, if the class has "shared identity" of instances in the whole image (SmallIntegers, Symbols...)

Petr Fischer petr.fischer at me.com
Wed Feb 20 18:28:27 EST 2019


> It is not clear to me what the semantics of such a selector would be.
> Consider this example:
>  t := [:x | x copy == x].
>  a := t value: 1.0e38.
>  b := t value: 1.0e308.
> What do you expect a and b to be?
> GNU Smalltalk: a=true, b=true.
> My Smalltalk, 32-bit or 64-bit: a=true, b=true.
> Squeak/Pharo, 32-bit: a=false, b=false.
> Squeak/Pharo, 64-bit: a=true, b=false.
> Squeak/Pharo, after a patch: a=true, b=true.
> 
> There are two quite different reasons why x copy == x
> might be true:
> * x is immutable (including its parts), and can be
>   thought of as a mathematical value, so that there
>   is no need to copy it
>   Examples: every kind of number, characters,
>   booleans, immutable collections, block closures
> * x is a way of accessing a unique resource, and
>   should not be copied, so making copy the identity
>   is a safety measure.
>   Examples: Semaphores, Mutexes, SharedQueues, data base
>   connections, some kinds of streams, singletons.
> * Laziness or error (inherited method not revised).
> 
> What is your use case?

I see... My use case was too superficial - thanks for answer!

pf

> 
> On Thu, 21 Feb 2019 at 07:32, Petr Fischer via Pharo-users <
> pharo-users at lists.pharo.org> wrote:
> 
> > Hello, some classes, like Symbols or SmallIntegers, shares identity of
> > value instances in the whole image (I may say it wrong), so:
> >
> > 1 == 1 copy. [true]
> > #aaa == #aaa copy. [true]
> >
> > all other classes not, like Strings, Objects etc., so:
> >
> > 'aaa' == 'aaa' copy. [false]
> >
> > Is there any test method (maybe on the class side) I could ask for this
> > (isXXX)?
> >
> > Thanks! pf
> >
> >



More information about the Pharo-users mailing list