Devel::Symdump - doubts in the output got.

sathiya.sw has asked for the wisdom of the Perl Monks concerning the following question:

I am experimenting with the Devel::Symdump which is basically for dumping the symbol table.

My code is this:

use Devel::Symdump;

$obj = Devel::Symdump->rnew();
$string = $obj->as_string;
print $string . "\n";

print "What is this? $+\n";
print "What is this? $^O\n";
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And the output is:

arrays
        Carp::CARP_NOT
        Carp::EXPORT
        Carp::EXPORT_FAIL
        Carp::EXPORT_OK
        Carp::ISA
        Config::EXPORT
        Config::EXPORT_OK
        DB::args
        lib::ORIG_INC
        main::+
        main::-
        main::ARGV
        main::INC
        main::_
functions
        Carp::carp
        Carp::cluck
        Carp::confess
        Carp::croak
        Carp::export_fail
        Carp::longmess
        Carp::shortmess
        Config::AUTOLOAD
        Config::DESTROY
        Config::FETCH
        Config::TIEHASH
        Config::import
        Devel::Symdump::AUTOLOAD
        Devel::Symdump::DESTROY
        Devel::Symdump::_doit
        Devel::Symdump::_inh_tree
        Devel::Symdump::_isa_tree
        Devel::Symdump::_partdump
        Devel::Symdump::_symdump
        Devel::Symdump::as_HTML
        Devel::Symdump::as_string
        Devel::Symdump::diff
        Devel::Symdump::inh_tree
        Devel::Symdump::isa_tree
        Devel::Symdump::new
        Devel::Symdump::rnew
        DynaLoader::boot_DynaLoader
        Exporter::as_heavy
        Exporter::export
        Exporter::export_fail
        Exporter::export_ok_tags
        Exporter::export_tags
        Exporter::export_to_level
        Exporter::import
        Exporter::require_version
        Internals::HvREHASH
        Internals::SvREADONLY
        Internals::SvREFCNT
        Internals::hash_seed
        Internals::hv_clear_placeholders
        Internals::rehash_seed
        PerlIO::Layer::NoWarnings
        PerlIO::Layer::find
        PerlIO::get_layers
        Regexp::DESTROY
        UNIVERSAL::VERSION
        UNIVERSAL::can
        UNIVERSAL::isa
        attributes::bootstrap
        lib::_get_dirs
        lib::_nativize
        lib::import
        lib::unimport
        strict::bits
        strict::import
        strict::unimport
        utf8::decode
        utf8::downgrade
        utf8::encode
        utf8::is_utf8
        utf8::native_to_unicode
        utf8::unicode_to_native
        utf8::upgrade
        utf8::valid
        vars::import
        warnings::Croaker
        warnings::__chk
        warnings::bits
        warnings::enabled
        warnings::import
        warnings::register::import
        warnings::register::mkMask
        warnings::unimport
        warnings::warn
        warnings::warnif
hashes
        Carp::CarpInternal
        Carp::Internal
        Config::Config
        Exporter::Cache
        lib::Config
        main::@
        main::ENV
        main::INC
        main::SIG
        warnings::Bits
        warnings::DeadBits
        warnings::Offsets
ios
        Devel::Symdump::ENTRY
        main::ARGV
        main::STDERR
        main::STDIN
        main::STDOUT
        main::_
        main::stderr
        main::stdin
        main::stdout
packages
        CORE
        CORE::GLOBAL
        Carp
        Carp::Heavy
        Config
        DB
        Devel
        Devel::Symdump
        DynaLoader
        Exporter
        Exporter::Heavy
        File
        File::Spec
        IO
        IO::Handle
        Internals
        Mac
        Mac::FileSpec
        Mac::FileSpec::Unixish
        PerlIO
        PerlIO::Layer
        Regexp
        UNIVERSAL
        attributes
        lib
        strict
        utf8
        vars
        warnings
        warnings::register
scalars
        CORE::GLOBAL::
        Carp::CARP_NOT
        Carp::CarpInternal
        Carp::CarpLevel
        Carp::EXPORT
        Carp::EXPORT_FAIL
        Carp::EXPORT_OK
        Carp::Heavy::
        Carp::ISA
        Carp::Internal
        Carp::MaxArgLen
        Carp::MaxArgNums
        Carp::MaxEvalLen
        Carp::VERSION
        Carp::Verbose
        Carp::carp
        Carp::cluck
        Carp::confess
        Carp::croak
        Carp::export_fail
        Carp::longmess
        Carp::longmess_heavy
        Carp::shortmess
        Carp::shortmess_heavy
        Config::AUTOLOAD
        Config::BEGIN
        Config::Config
        Config::DESTROY
        Config::EXPORT
        Config::EXPORT_OK
        Config::FETCH
        Config::TIEHASH
        Config::config_re
        Config::config_sh
        Config::config_vars
        Config::import
        Config::launcher
        Config::myconfig
        DB::args
        Devel::Symdump::
        Devel::Symdump::AUTOLOAD
        Devel::Symdump::BEGIN
        Devel::Symdump::DESTROY
        Devel::Symdump::Defaults
        Devel::Symdump::ENTRY
        Devel::Symdump::MAX_RECURSION
        Devel::Symdump::VERSION
        Devel::Symdump::_doit
        Devel::Symdump::_inh_tree
        Devel::Symdump::_isa_tree
        Devel::Symdump::_partdump
        Devel::Symdump::_symdump
        Devel::Symdump::as_HTML
        Devel::Symdump::as_string
        Devel::Symdump::diff
        Devel::Symdump::import
        Devel::Symdump::inh_tree
        Devel::Symdump::isa_tree
        Devel::Symdump::new
        Devel::Symdump::rnew
        DynaLoader::boot_DynaLoader
        Exporter::Cache
        Exporter::Debug
        Exporter::ExportLevel
        Exporter::Heavy::
        Exporter::VERSION
        Exporter::Verbose
        Exporter::__ANON__
        Exporter::as_heavy
        Exporter::export
        Exporter::export_fail
        Exporter::export_ok_tags
        Exporter::export_tags
        Exporter::export_to_level
        Exporter::import
        Exporter::require_version
        File::Spec::
        IO::Handle::
        Internals::HvREHASH
        Internals::SvREADONLY
        Internals::SvREFCNT
        Internals::hash_seed
        Internals::hv_clear_placeholders
        Internals::rehash_seed
        Mac::FileSpec::
        Mac::FileSpec::Unixish::
        Mac::FileSpec::Unixish::nativize
        PerlIO::Layer::
        PerlIO::Layer::NoWarnings
        PerlIO::Layer::find
        PerlIO::get_layers
        Regexp::DESTROY
        UNIVERSAL::VERSION
        UNIVERSAL::can
        UNIVERSAL::import
        UNIVERSAL::isa
        attributes::bootstrap
        lib::BEGIN
        lib::Config
        lib::ORIG_INC
        lib::VERSION
        lib::_get_dirs
        lib::_nativize
        lib::import
        lib::unimport
        main::^H
        main::^O
        main::^R
        main::^V
        main::^W
        main::^WARNING_BITS
        main::^X
        main::!
        main::"
        main::$
        main::+
        main::-
        main::/
        main::0
        main::1
        main::<none>::
        main::@
        main::ARGV
        main::BEGIN
        main::CORE::
        main::Carp::
        main::Config::
        main::DB::
        main::Devel::
        main::DynaLoader::
        main::ENV
        main::Exporter::
        main::File::
        main::INC
        main::IO::
        main::Internals::
        main::Mac::
        main::PerlIO::
        main::Regexp::
        main::SIG
        main::STDERR
        main::STDIN
        main::STDOUT
        main::UNIVERSAL::
        main::]
        main::_
        main::_<perlio.c
        main::_<perlmain.c
        main::_<universal.c
        main::_<xsutils.c
        main::attributes::
        main::lib::
        main::main::
        main::obj
        main::stderr
        main::stdin
        main::stdout
        main::strict::
        main::string
        main::utf8::
        main::vars::
        main::warnings::
        strict::VERSION
        strict::bits
        strict::import
        strict::unimport
        utf8::decode
        utf8::downgrade
        utf8::encode
        utf8::is_utf8
        utf8::native_to_unicode
        utf8::unicode_to_native
        utf8::upgrade
        utf8::valid
        vars::BEGIN
        vars::VERSION
        vars::import
        warnings::All
        warnings::BEGIN
        warnings::BYTES
        warnings::Bits
        warnings::Croaker
        warnings::DeadBits
        warnings::LAST_BIT
        warnings::NONE
        warnings::Offsets
        warnings::VERSION
        warnings::__chk
        warnings::bits
        warnings::enabled
        warnings::import
        warnings::register::
        warnings::register::VERSION
        warnings::register::import
        warnings::register::mkMask
        warnings::unimport
        warnings::warn
        warnings::warnif
unknowns

What is this?
What is this? linux
[download]

Here are my questions.

Arrays prints under arrays. Hashes prints under hash - It is ok.
1. But Why does most of the identifiers are getting printed under the scalars. ( check some package names are also printed under the scalars, if it is printed under packages it is right, but why here ?? )

2. Only the package names ends with :: in the identifier, why is it so ?? others does not.

3. While trying to print the scalars, some got printed and some does not. Why +, - are used as default, and what is the use of it. ??

Sathiya

Comment on Devel::Symdump - doubts in the output got. Select or Download Code

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Re: Devel::Symdump - doubts in the output got. by gone2015 (Deacon) on Dec 08, 2008 at 11:29 UTC
1. But Why does most of the identifiers are getting printed under the scalars. ( check some package names are also printed under the scalars, if it is printed under packages it is right, but why here ?? ) I suspect that all the identifiers are getting printed under "scalars"... Background: the entry for an identifier is a reference to a GLOB (unless it's a late model 'constant', in which case it may be a reference to a SCALAR, ARRAY or HASH). A GLOB contains a pointer to the various different things that the identifier may refer to -- SCALAR, ARRAY, HASH, CODE, etc -- and the (eg) `foo{HASH}` construct will return the respective pointer. Kicker: for everything except SCALAR, (eg) `foo{HASH}` will return `undef` when no HASH has been defined. For SCALAR the pointer is always defined, but the value it points to may be `undef`. This means that it's not possible to distinguish between a SCALAR that has been declared but whose value is `undef`, and a SCALAR that has never actually been declared. I had a look at Devel::Symdump. It thinks that a SCALAR exists if the pointer `ENTRY{SCALAR}` is defined. It could test to see if what is pointed to is also defined, but then it would miss a declared SCALAR which has not yet been defined. There just isn't a completely right answer to this :-( 2. Only the package names ends with :: in the identifier, why is it so ?? others does not.* This is easier... you may be thinking of the '`::`' as separators. In effect they are part of the package name. But, since they come at the end of the name they can also be treated as separators... 3. While trying to print the scalars, some got printed and some does not. Why +, - are used as default, and what is the use of it. ?? I'm sorry, you lost me here... If you mean that you tried printing the scalar value of everything listed as a Scalar by Devel::Symdump, then the above explains why many will have `undef` SCALAR parts. As for what `$+` and `$^O` are, I refer you to perlvar.	[reply] [d/l] [select]

Replies are listed 'Best First'.

Re: Devel::Symdump - doubts in the output got.
by gone2015 (Deacon) on Dec 08, 2008 at 11:29 UTC

1. But Why does most of the identifiers are getting printed under the scalars. ( check some package names are also printed under the scalars, if it is printed under packages it is right, but why here ?? )

I suspect that all the identifiers are getting printed under "scalars"...

Background: the entry for an identifier is a reference to a GLOB (unless it's a late model 'constant', in which case it may be a reference to a SCALAR, ARRAY or HASH). A GLOB contains a pointer to the various different things that the identifier may refer to -- SCALAR, ARRAY, HASH, CODE, etc -- and the (eg) *foo{HASH} construct will return the respective pointer.

Kicker: for everything except SCALAR, (eg) *foo{HASH} will return undef when no HASH has been defined. For SCALAR the pointer is always defined, but the value it points to may be undef. This means that it's not possible to distinguish between a SCALAR that has been declared but whose value is undef, and a SCALAR that has never actually been declared.

I had a look at Devel::Symdump. It thinks that a SCALAR exists if the pointer *ENTRY{SCALAR} is defined. It could test to see if what is pointed to is also defined, but then it would miss a declared SCALAR which has not yet been defined. There just isn't a completely right answer to this :-(

2. Only the package names ends with :: in the identifier, why is it so ?? others does not.

This is easier... you may be thinking of the '::' as separators. In effect they are part of the package name. But, since they come at the end of the name they can also be treated as separators...

3. While trying to print the scalars, some got printed and some does not. Why +, - are used as default, and what is the use of it. ??

I'm sorry, you lost me here... If you mean that you tried printing the scalar value of everything listed as a Scalar by Devel::Symdump, then the above explains why many will have undef SCALAR parts.

As for what $+ and $^O are, I refer you to perlvar.

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