[albany-pm] Typeglobs help!

[Mark Fowler]

I had a think about it some more while I was loading the dishwasher.

Maybe you could get away with some magic here?

sub dualvar { return Dualvar->new( @_ ) }

package Dualvar;

use overload '""' => 'str', '+0' => 'num';

sub new {
  my $class = shift;
  return bless {
    Num => shift,
    Str => shift
  }, $class
}

sub num { shift->{Num} }
sub str { shift->{Str} }

Etc etc. you'd need to implement is_dual too

Problems:

- ref would give you the wrong value.
- blessed would give you the wrong thing
- anything using XS would need to respect the overloading magic by hand,
which it probably won't

Ymmv.

Personally I'd either shell out to binary ssh or use a custom Perl instead

Mark
(Code not tested, typed in iPhone, treat accordingly)




On Thursday, March 27, 2014, Mark Fowler <mark at twoshortplanks.com> wrote:

> Ah Patrick, I've got bad news for you...
>
> You're mixing up typeglobs and scalars. A typeglob is essentially a symbol
> table entry that holds everything with different sidles.  So the *foo
> typeglob holds $foo, @foo, &foo, %foo, etc, etc.
>
> A scalar is little C struct[1] that holds a integer value, a floating
> point value, a pointer to a string, etc etc and a set of flags indicating
> which of these are valid or not. Whenever Perl needs a different kind of
> value - say the sting form of some scalar computed by a numerical
> calculation - it converts the value from one of the other forms and stores
> it back in the scalar and marks the flags to indicate that right now both
> values are good and Perl doesn't need to do any conversion.
>
> A dualvar is essentially a scalar where you can manually set the string
> part and numerical part of the scalar by hand to different values.
>
> So, no we can't use typeglobs because typeglobs only have one entry for a
> scalar in them, not a separate scalar for numerical and string values.
>
> To make matters worse, there's no way as far as I know to access the
> various parts of a scalar from Perl space without using some XS code.
>
> Possible further solutions:
>
> - ask for help with Net::SSH
> - shell out to the system ssh binary, possibly using an Expect command if
> you need to
> - install a custom Perl just for this task. perlbrew is your friend here.
>
> Mark
>
> [1] technically a set of structs depending on how it's being used, but
> that's not important right now.
>
> On Thursday, March 27, 2014, Patrick Cronin <oshihuna at gmail.com<javascript:_e(%7B%7D,'cvml','oshihuna at gmail.com');>>
> wrote:
>
>> I manage a CentOS 5.10 server running perl 5.8.8. For <REASONS>, I can't
>> upgrade it.
>>
>> For some reason, I can't install the XS version of Scalar::Util, and so
>> I'm stuck using the PP version. Net::OpenSSH relies on Scalar::Util's
>> dualvar function (which is only available in the XS version of
>> Scalar::Util) to create a single scalar holding both an integer and string
>> value. When the scalar is used in a numeric context, the integer value
>> comes out, and when the scalar is used in a string context, the string
>> value comes out. I'm trying to write a quick and dirty PP version of
>> dualvar so I can move on with my life.
>>
>> I seem to remember seeing this being done, but no amount of googling is
>> getting me there. I've looked up typeglobs and the *foo{THING} construct,
>> but while THING can be SCALAR, it can't be NUMBER or STRING. Does anyone
>> know the magic to make this happen?
>>
>> I'm trying variations of the following:
>>
>> my $int = 2;
>> my $string = "test";
>>
>> my $typeglob = $int;
>> *typeglob{SCALAR} = ${ *string };
>>
>> print ($typeglob + 2) . "\n";
>> print $typeglob . " YES!\n";
>>
>> It just feels gross, and it's not working.
>>
>> Does anyone have the magic?
>>
>> ------------------------------
>> [image: Patrick's Avatar] *Patrick Cronin*
>> Computer Lover
>> Mobile: +1 518 336 5133
>> Email: oshihuna at gmail.com
>> Skype: patrickcronin12061
>>
>> P Please consider the environment before printing this e-mail /
>> attachments
>>
>>
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