Re: [htmltmpl] Patch to fix global_vars and loop problem...

[Mathew R. <mat...@re...>]

> > here you create a global variable called 'gvar'
> > > $t->param(gvar     =3D> "global variable");
> >=20
> > here you are creating a loop specific variable called 'gvar'
> > >     { loopvar =3D> "GVar should be set",         gvar =3D> "Loop =
GVar 1" },
> >=20
> > These two 'gvar's are two different variables.=20
> >=20
> > In this case
> > >     { loopvar =3D> "GVar should be blank again", gvar =3D> undef   =
      },
> >=20
> > you are saying that the loop specific 'gvar' is not part of the loop =
- ie equivalent to:
> >        { loopvar =3D> "GVar should be blank again" }
>=20
> here is where i think we differ...=20
>=20
> 1. $href =3D { loopvar =3D> "GVar should be blank again", gvar =3D> =
undef }
> to me (and in general perl programming is VERY different from:=20
> 2. $href =3D { loopvar =3D> "GVar should be blank again" }

umm... not quite... Perl treats 'unknown' and 'undef' as the same thing =
if "use strict" is in effect (which it always should be) - and this is a =
compile-time test. (Aside:  I think 'exists' on a plain scalar / =
array_ref would solve this problem - but Perl doesn't have that =
capability).

Perl will try to lookup 'gvar' in its symbol table.  If the value =
doesn't exist in the symbol table, then any use of the 'gvar' gets =
flagged as a warning - this is a run-time test.

Hash'es on the other hand, always get autovivified, thus 'exists' makes =
sense.

Relating this to TMPL_LOOP's... the question becomes, "Is a variable =
inside a loop considered to be equivalent to a hash key, or equivalent =
to a variable?", alternatively it could be asked "What is the =
'strict'ness of TMPL_LOOP variables (as compared to Perl's use of =
'strict'ness)?".
=20
> In (1), you are explicitely saying that you want "gvar" to be =
undefined.
> In (2), you are not saying that... you are effectively saying that you
> don't care what "gvar" is...

no - in (2) I said nothing about gvar - I didn't say "I dont care"
=20
> To see how perl treats them differently, here is an example of a very
> common function (keys) that returns all the keys in a hash...=20
>=20
> (1) perl  > print "Keys: ". join(',', keys %$href) . "\n";
> (1) output> Keys: gvar,loopvar
>=20
> (2) perl  > print "Keys: ". join(',', keys %$href) . "\n";
> (2) output> Keys: loopvar

Since we are talking about TMPL_LOOP variables, not Perl hash keys, it =
gets back to the question(s) posed above.

> Another example:
>=20
> -- test.pl --
> #!/usr/bin/perl
> my $tvar =3D "this is a test";
> $tvar =3D undef;
> print "Tvar=3D$tvar\n";
> -----------------------------------------
> The above prints: Tvar=3D

true - but only if you dont do:

use strict;
use warnings;

... and I cant find a single reference suggesting to not use the 'use's.


> Now, so in the same context if "undef" should mean... take the outer
> scope, then perl should have ignored my "$tvar =3D undef" line...=20

No - setting a value to 'undef' means - "remove me from the symbol =
table" - it doesnt mean, "make my value to be 'undef'" (although you get =
this behaviour if 'use strict' is not in effect).


> I think its definitely a bug :-)=20
> It has infact been flagged before as well... its partially on a thread
> at:
> =
http://www.mail-archive.com/htm...@li.../msg=
00728.html
> although that thread digressed a bit... but this topic has been bought
> up a few times... so maybe we can find more threads about it in the
> history of the list...=20

fair enough - although, that doesn't constitute a reason to modify the =
behaviour.  A change to the code, should require us to agree on the =
answer to the question(s) posed above.

Mathew


>=20
>=20
>=20
>=20
>=20
> >=20
> > thus requesting the outer global gvar to come into scope.
> >=20
> > Consider:
> >=20
> > t->param(gvar =3D> "Global gvar");
> > my $gvar_val;
> > my @loop;
> > for.... {
> >   if (something) {
> >     $gvar_val =3D "Loop GVar 1";
> >   } elsif (somethign else) {
> >     $gvar_val =3D "";
> >   }
> >   my $tmp;
> >   $tmp->{loopvar} =3D ...;
> >   $tmp->{gvar} =3D $gvar;
> >   push @loop, $tmp;
> > }
> > t->param(testloop =3D>\@loop);
> >=20
> > What would you expect the TMPL_LOOP to do in that example?=20
> > I would have expected that the third iteration to use the global =
gvar value.
> >=20
> > Mathew
> >=20
> >=20
> > > =
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> > > test.tmpl:
> > > ----------
> > > Global Variable gvar is: <tmpl_var name=3Dgvar>
> > >=20
> > > Loop: <tmpl_loop name=3Dtestloop>
> > >         loopvar: <tmpl_var name=3Dloopvar>
> > >         gvar   : <tmpl_var name=3Dgvar>
> > >       </tmpl_loop>
> > > =
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> > > test.pl
> > > -------
> > >=20
> > > use strict;
> > > use HTML::Template;
> > >=20
> > > my $t =3D new HTML::Template(filename =3D> "test.tmpl", =
global_vars =3D> 1,)
> > > || die;
> > >=20
> > > my $testloop =3D [
> > >     { loopvar =3D> "GVar should be set",         gvar =3D> "Loop =
GVar 1" },
> > >     { loopvar =3D> "GVar should be blank",       gvar =3D> ""      =
      },
> > >     { loopvar =3D> "GVar should be blank again", gvar =3D> undef   =
      },
> > > ];
> > >=20
> > > $t->param(gvar     =3D> "global variable");
> > > $t->param(testloop =3D> $testloop);
> > > print $t->output();
> > > =
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> > >=20
> > > When you run test.pl.. you get the following output:
> > > =
------------------------------------------------------------------------
> > > Global Variable gvar is: global variable
> > >=20
> > > Loop:=20
> > >         loopvar: GVar should be set=20
> > >         gvar   : Loop GVar 1
> > >      =20
> > >         loopvar: GVar should be blank
> > >         gvar   :=20
> > >      =20
> > >         loopvar: GVar should be blank again
> > >         gvar   : global variable
> > > =
------------------------------------------------------------------------
> > >=20
> > > Now, the issue is that "gvar" in the third iteration of the loop,
> > > "should have been blank"... i explicitely set it to "undef" in the
> > > code.. however, since global_vars was on, it ignored my "undef".=20
>=20
>=20
>