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Re: Thoughts Towards Type Assertions (was: Re: Pre-RFC: builtin::functions for detecting numbers vs strings)

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From:
Paul "LeoNerd" Evans
Date:
February 25, 2022 15:19
Subject:
Re: Thoughts Towards Type Assertions (was: Re: Pre-RFC: builtin::functions for detecting numbers vs strings)
Message ID:
20220225151904.69769869@shy.leonerd.org.uk
On Fri, 25 Feb 2022 15:55:00 +0900
Yuki Kimoto <kimoto.yuki@gmail.com> wrote:

> 2022-2-25 1:31 Paul "LeoNerd" Evans <leonerd@leonerd.org.uk> wrote:
> 
> >
> >   * We've finished the PV vs. IVNV split that PR #18958 began, so
> > now we can perfectly remember "was originally a string" vs "was
> >     originally a number".
> >
> >  
> A Perl big problem is that when a value is touched, the type of value
> is changed.
> 
> When a value is created or updated, the type of value is created or
> changed. This is understandable.
> 
> However, in current Perl, only touching a value changes the type of
> the value. This is strange.
> 
> This reason is that the type of value is used internally and the type
> is changed freely.
> 
> Is it possible to design the user type that is not affected by
> touching?
> 
> I think it's important that the types of the number and string don't
> change unintentionally.

That is the entire point of the above-mentioned PR, yes.

It stops perl adding the (public) SvPOK flag to SVs as a side-effect of
looking at their stringy value. It means that values which started off
numeric *remain* numeric and never gain that SvPOK flag, meaning you
can now reliably distinguish that they originally started off as a
number.

-- 
Paul "LeoNerd" Evans

leonerd@leonerd.org.uk      |  https://metacpan.org/author/PEVANS
http://www.leonerd.org.uk/  |  https://www.tindie.com/stores/leonerd/

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