UNIVERSAL::can reports that undef is an object?

[p5pRT]

Migrated from rt.perl.org#2110 (status was 'resolved')

Searchable as RT2110$

[p5pRT]

From sburke@stonehenge.netadventure.net

Each of these
  $x = 123; print UNIVERSAL​::isa($x, "UNIVERSAL") ? 'T' : 'F';
  $x = 'fish'; print UNIVERSAL​::isa($x, "UNIVERSAL") ? 'T' : 'F';
  $x = undef; print UNIVERSAL​::isa($x, "Stuff" ) ? 'T' : 'F';
do print 'F', as expected.

But this
  $x = undef; print UNIVERSAL​::isa($x, "UNIVERSAL") ? 'T' : 'F';
prints 'T'.

UNIVERSAL​::isa ( VAL, TYPE )
isa returns true if the first argument is a reference and either of
the following statements is true.

  VAL is a blessed reference and is blessed into package TYPE or
  inherits from package TYPE

  VAL is a reference to a TYPE of perl variable (er 'HASH')

I take the "if" to mean "if and only if", so
UNIVERSAL​::isa(undef, anything) should return false.

Also, I suggest s/er/e.g./, and s/perl/Perl/ in the text there.

--
Sean M. Burke sburke@​netadventure.net http​://www.netadventure.net/~sburke/

[p5pRT]

From [Unknown Contact. See original ticket]

Whoops, I forgot to note my version of Perl. It's​:

% perl -V
Summary of my perl5 (5.0 patchlevel 5 subversion 3) configuration​:
  Platform​:
  osname=aix, osvers=4.3.1.0, archname=aix
  uname='aix pegasus 3 4 000165185700 '
  hint=recommended, useposix=true, d_sigaction=define
  usethreads=undef useperlio=undef d_sfio=undef
  Compiler​:
  cc='cc', optimize='-O', gccversion=
  cppflags='-D_ALL_SOURCE -D_ANSI_C_SOURCE -D_POSIX_SOURCE -qmaxmem=8192 -I/usr/local/include -I/usr/local/gnu/include'
  ccflags ='-D_ALL_SOURCE -D_ANSI_C_SOURCE -D_POSIX_SOURCE -qmaxmem=8192 -I/usr/local/include -I/usr/local/gnu/include'
  stdchar='unsigned char', d_stdstdio=define, usevfork=false
  intsize=4, longsize=4, ptrsize=4, doublesize=8
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=8
  alignbytes=8, usemymalloc=n, prototype=define
  Linker and Libraries​:
  ld='ld', ldflags ='-L/usr/local/lib -L/usr/local/gnu/lib -L/usr/ccs/lib -L/lib'
  libpth=/usr/local/lib /lib /usr/lib /usr/ccs/lib /usr/local/gnu/lib
  libs=-lnsl -lgdbm -ldbm -ldl -lld -lm -lc -lcrypt -lbsd -lPW
  libc=, so=a, useshrplib=false, libperl=libperl.a
  Dynamic Linking​:
  dlsrc=dl_aix.xs, dlext=so, d_dlsymun=undef, ccdlflags='-bE​:perl.exp'
  cccdlflags=' ', lddlflags='-bhalt​:4 -bM​:SRE -bI​:$(PERL_INC)/perl.exp -bE​:$(BASEEXT).exp -b noentry -lc -L/usr/local/lib -L/usr/local/gnu/lib -L/usr/ccs/lib -L/lib'

Characteristics of this binary (from libperl)​:
  Built under aix
  Compiled at Aug 12 1999 09​:10​:29
  %ENV​:
  PERLLIB="/nfs/user/l/lachler/.bin/perl"
  @​INC​:
  /nfs/user/l/lachler/.bin/perl
  /usr/local/gnu/lib/perl5/5.00503/aix
  /usr/local/gnu/lib/perl5/5.00503
  /usr/local/gnu/lib/perl5/site_perl/5.005/aix
  /usr/local/gnu/lib/perl5/site_perl/5.005
  .

--
Sean M. Burke sburke@​netadventure.net http​://www.netadventure.net/~sburke/

[p5pRT]

From @ysth

In article <200002070122.RAA22777@​stonehenge.netadventure.net>,
"Sean M. Burke" <sburke@​stonehenge.netadventure.net> wrote​:

Each of these
$x = 123; print UNIVERSAL​::isa($x, "UNIVERSAL") ? 'T' : 'F';
$x = 'fish'; print UNIVERSAL​::isa($x, "UNIVERSAL") ? 'T' : 'F';
$x = undef; print UNIVERSAL​::isa($x, "Stuff" ) ? 'T' : 'F';
do print 'F', as expected.

But this
$x = undef; print UNIVERSAL​::isa($x, "UNIVERSAL") ? 'T' : 'F';
prints 'T'.

Not a bug. The undef is treated as '' (with the usual warning, for
folks that believe in warnings), and '' is another name for 'main'.
'main' indeed isa 'UNIVERSAL'.

Also note this​:
{ package fish; package Stuff } # Make some packages
${"123​::foo"} = 1; # Create an 'illegal' package name
@​​::ISA = 'Stuff'; # Note the package name
$x = 123; print UNIVERSAL​::isa($x, "UNIVERSAL") ? 'T' : 'F';
$x = 'fish'; print UNIVERSAL​::isa($x, "UNIVERSAL") ? 'T' : 'F';
$x = undef; print UNIVERSAL​::isa($x, "Stuff" ) ? 'T' : 'F';

Now they all print 'T', as expected.

UNIVERSAL​::isa ( VAL, TYPE )
isa returns true if the first argument is a reference and either of
the following statements is true.

VAL is a blessed reference and is blessed into package TYPE or
inherits from package TYPE

VAL is a reference to a TYPE of perl variable (er 'HASH')

I take the "if" to mean "if and only if", so
UNIVERSAL​::isa(undef, anything) should return false.

Also, I suggest s/er/e.g./, and s/perl/Perl/ in the text there.

Here's a patch​:

Inline Patch

--- UNIVERSAL.pm-pre	Wed Jan 26 21:38:52 2000
+++ UNIVERSAL.pm	Mon Feb  7 09:25:50 2000
@@ -62,19 +62,23 @@
 
 =item UNIVERSAL::isa ( VAL, TYPE )
 
-C<isa> returns I<true> if the first argument is a reference and either
-of the following statements is true.
+C<isa> returns I<true> if one of the following statements is true.
 
 =over 8
 
 =item *
 
-C<VAL> is a blessed reference and is blessed into package C<TYPE>
-or inherits from package C<TYPE>
+C<VAL> is a reference blessed into either package C<TYPE> or a package
+which inherits from package C<TYPE>.
 
 =item *
 
-C<VAL> is a reference to a C<TYPE> of perl variable (er 'HASH')
+C<VAL> is a reference to a C<TYPE> of Perl variable (e.g. 'HASH').
+
+=item *
+
+C<VAL> is the name of a package that inherits from (or is itself)
+package C<TYPE>.
 
 =back
 

[p5pRT]

From @gbarr

No, isa and can should do the same as a normal method call and
both of the following fail

$ perl -e '$p->VERSION'
Can't call method "VERSION" on an undefined value at -e line 1.
$ perl -e '$p=""; $p->VERSION'
Can't call method "VERSION" without a package or object reference at -e line 1.

So isa and can should to the same. Here is a patch

Inline Patch

--- universal.c.orig	Tue Feb  8 15:12:42 2000
+++ universal.c	Tue Feb  8 15:23:55 2000
@@ -140,6 +140,10 @@
 	Perl_croak(aTHX_ "Usage: UNIVERSAL::isa(reference, kind)");
 
     sv = ST(0);
+
+    if (!SvOK(sv) || !SvCUR(sv))
+	XSRETURN_UNDEF;
+
     name = (char *)SvPV(ST(1),n_a);
 
     ST(0) = boolSV(sv_derived_from(sv, name));
@@ -159,6 +163,10 @@
 	Perl_croak(aTHX_ "Usage: UNIVERSAL::can(object-ref, method)");
 
     sv = ST(0);
+
+    if (!SvOK(sv) || !SvCUR(sv))
+	XSRETURN_UNDEF;
+
     name = (char *)SvPV(ST(1),n_a);
     rv = &PL_sv_undef;
 

On Mon, Feb 07, 2000 at 10:51:43AM -0800, Yitzchak Scott-Thoennes wrote: > In article \<200002070122\.RAA22777@​stonehenge\.netadventure\.net>\, > "Sean M\. Burke" \ wrote​: > >Each of these > > $x = 123; print UNIVERSAL​::isa\($x\, "UNIVERSAL"\) ? 'T' : 'F'; > > $x = 'fish'; print UNIVERSAL​::isa\($x\, "UNIVERSAL"\) ? 'T' : 'F'; > > $x = undef; print UNIVERSAL​::isa\($x\, "Stuff" \) ? 'T' : 'F'; > >do print 'F'\, as expected\. > > > >But this > > $x = undef; print UNIVERSAL​::isa\($x\, "UNIVERSAL"\) ? 'T' : 'F'; > >prints 'T'\. > > Not a bug\. The undef is treated as '' \(with the usual warning\, for > folks that believe in warnings\)\, and '' is another name for 'main'\. > 'main' indeed isa 'UNIVERSAL'\. > > Also note this​: > \{ package fish; package Stuff \} \# Make some packages > $\{"123​::foo"\} = 1; \# Create an 'illegal' package name > @​​::ISA = 'Stuff'; \# Note the package name > $x = 123; print UNIVERSAL​::isa\($x\, "UNIVERSAL"\) ? 'T' : 'F'; > $x = 'fish'; print UNIVERSAL​::isa\($x\, "UNIVERSAL"\) ? 'T' : 'F'; > $x = undef; print UNIVERSAL​::isa\($x\, "Stuff" \) ? 'T' : 'F'; > > Now they all print 'T'\, as expected\. > > >UNIVERSAL​::isa \( VAL\, TYPE \) > > isa returns true if the first argument is a reference and either of > > the following statements is true\. > > > > VAL is a blessed reference and is blessed into package TYPE or > > inherits from package TYPE > > > > VAL is a reference to a TYPE of perl variable \(er 'HASH'\) > > > >I take the "if" to mean "if and only if"\, so > >UNIVERSAL​::isa\(undef\, anything\) should return false\. > > > >Also\, I suggest s/er/e\.g\./\, and s/perl/Perl/ in the text there\. > > Here's a patch​: > > \-\-\- UNIVERSAL\.pm\-pre Wed Jan 26 21​:38​:52 2000 > \+\+\+ UNIVERSAL\.pm Mon Feb 7 09​:25​:50 2000 > @​@​ \-62\,19 \+62\,23 @​@​ > > =item UNIVERSAL​::isa \( VAL\, TYPE \) > > \-C\ returns I\ if the first argument is a reference and either > \-of the following statements is true\. > \+C\ returns I\ if one of the following statements is true\. > > =over 8 > > =item \* > > \-C\ is a blessed reference and is blessed into package C\ > \-or inherits from package C\ > \+C\ is a reference blessed into either package C\ or a package > \+which inherits from package C\\. > > =item \* > > \-C\ is a reference to a C\ of perl variable \(er 'HASH'\) > \+C\ is a reference to a C\ of Perl variable \(e\.g\. 'HASH'\)\. > \+ > \+=item \* > \+ > \+C\ is the name of a package that inherits from \(or is itself\) > \+package C\\. > > =back >

[p5pRT]

From @gbarr

Whoops, posted before testing. This patch is right.

Graham.

Inline Patch

--- universal.c.orig	Tue Feb  8 15:12:42 2000
+++ universal.c	Tue Feb  8 15:41:09 2000
@@ -140,6 +140,10 @@
 	Perl_croak(aTHX_ "Usage: UNIVERSAL::isa(reference, kind)");
 
     sv = ST(0);
+
+    if (!SvOK(sv) || !(SvROK(sv) || SvCUR(sv)))
+	XSRETURN_UNDEF;
+
     name = (char *)SvPV(ST(1),n_a);
 
     ST(0) = boolSV(sv_derived_from(sv, name));
@@ -159,6 +163,10 @@
 	Perl_croak(aTHX_ "Usage: UNIVERSAL::can(object-ref, method)");
 
     sv = ST(0);
+
+    if (!SvOK(sv) || !(SvROK(sv) || SvCUR(sv)))
+	XSRETURN_UNDEF;
+
     name = (char *)SvPV(ST(1),n_a);
     rv = &PL_sv_undef;
 

On Tue, Feb 08, 2000 at 03:25:14PM +0000, Graham Barr wrote: > No\, isa and can should do the same as a normal method call and > both of the following fail > > $ perl \-e '$p\->VERSION' > Can't call method "VERSION" on an undefined value at \-e line 1\. > $ perl \-e '$p=""; $p\->VERSION' > Can't call method "VERSION" without a package or object reference at \-e line 1\. > > So isa and can should to the same\. Here is a patch > > \-\-\- universal\.c\.orig Tue Feb 8 15​:12​:42 2000 > \+\+\+ universal\.c Tue Feb 8 15​:23​:55 2000 > @​@​ \-140\,6 \+140\,10 @​@​ > Perl\_croak\(aTHX\_ "Usage​: UNIVERSAL​::isa\(reference\, kind\)"\); > > sv = ST\(0\); > \+ > \+ if \(\!SvOK\(sv\) || \!SvCUR\(sv\)\) > \+ XSRETURN\_UNDEF; > \+ > name = \(char \*\)SvPV\(ST\(1\)\,n\_a\); > > ST\(0\) = boolSV\(sv\_derived\_from\(sv\, name\)\); > @​@​ \-159\,6 \+163\,10 @​@​ > Perl\_croak\(aTHX\_ "Usage​: UNIVERSAL​::can\(object\-ref\, method\)"\); > > sv = ST\(0\); > \+ > \+ if \(\!SvOK\(sv\) || \!SvCUR\(sv\)\) > \+ XSRETURN\_UNDEF; > \+ > name = \(char \*\)SvPV\(ST\(1\)\,n\_a\); > rv = &PL\_sv\_undef; > > On Mon\, Feb 07\, 2000 at 10​:51​:43AM \-0800\, Yitzchak Scott\-Thoennes wrote​: > > In article \<200002070122\.RAA22777@​stonehenge\.netadventure\.net>\, > > "Sean M\. Burke" \ wrote​: > > >Each of these > > > $x = 123; print UNIVERSAL​::isa\($x\, "UNIVERSAL"\) ? 'T' : 'F'; > > > $x = 'fish'; print UNIVERSAL​::isa\($x\, "UNIVERSAL"\) ? 'T' : 'F'; > > > $x = undef; print UNIVERSAL​::isa\($x\, "Stuff" \) ? 'T' : 'F'; > > >do print 'F'\, as expected\. > > > > > >But this > > > $x = undef; print UNIVERSAL​::isa\($x\, "UNIVERSAL"\) ? 'T' : 'F'; > > >prints 'T'\. > > > > Not a bug\. The undef is treated as '' \(with the usual warning\, for > > folks that believe in warnings\)\, and '' is another name for 'main'\. > > 'main' indeed isa 'UNIVERSAL'\. > > > > Also note this​: > > \{ package fish; package Stuff \} \# Make some packages > > $\{"123​::foo"\} = 1; \# Create an 'illegal' package name > > @​​::ISA = 'Stuff'; \# Note the package name > > $x = 123; print UNIVERSAL​::isa\($x\, "UNIVERSAL"\) ? 'T' : 'F'; > > $x = 'fish'; print UNIVERSAL​::isa\($x\, "UNIVERSAL"\) ? 'T' : 'F'; > > $x = undef; print UNIVERSAL​::isa\($x\, "Stuff" \) ? 'T' : 'F'; > > > > Now they all print 'T'\, as expected\. > > > > >UNIVERSAL​::isa \( VAL\, TYPE \) > > > isa returns true if the first argument is a reference and either of > > > the following statements is true\. > > > > > > VAL is a blessed reference and is blessed into package TYPE or > > > inherits from package TYPE > > > > > > VAL is a reference to a TYPE of perl variable \(er 'HASH'\) > > > > > >I take the "if" to mean "if and only if"\, so > > >UNIVERSAL​::isa\(undef\, anything\) should return false\. > > > > > >Also\, I suggest s/er/e\.g\./\, and s/perl/Perl/ in the text there\. > > > > Here's a patch​: > > > > \-\-\- UNIVERSAL\.pm\-pre Wed Jan 26 21​:38​:52 2000 > > \+\+\+ UNIVERSAL\.pm Mon Feb 7 09​:25​:50 2000 > > @​@​ \-62\,19 \+62\,23 @​@​ > > > > =item UNIVERSAL​::isa \( VAL\, TYPE \) > > > > \-C\ returns I\ if the first argument is a reference and either > > \-of the following statements is true\. > > \+C\ returns I\ if one of the following statements is true\. > > > > =over 8 > > > > =item \* > > > > \-C\ is a blessed reference and is blessed into package C\ > > \-or inherits from package C\ > > \+C\ is a reference blessed into either package C\ or a package > > \+which inherits from package C\\. > > > > =item \* > > > > \-C\ is a reference to a C\ of perl variable \(er 'HASH'\) > > \+C\ is a reference to a C\ of Perl variable \(e\.g\. 'HASH'\)\. > > \+ > > \+=item \* > > \+ > > \+C\ is the name of a package that inherits from \(or is itself\) > > \+package C\\. > > > > =back > >