The B module supplies classes which allow a Perl program to delve
into its own innards. It is the module used to implement the
``backends'' of the Perl compiler. Usage of the compiler does not
require knowledge of this module: see the O module for the
user-visible part. The B module is of use to those who want to
write new compiler backends. This documentation assumes that the
reader knows a fair amount about perl's internals including such
things as SVs, OPs and the internal symbol table and syntax tree
of a program.
The B module contains a set of utility functions for querying the
current state of the Perl interpreter; typically these functions
return objects from the B::SV and B::OP classes, or their derived
classes. These classes in turn define methods for querying the
resulting objects about their own internal state.
The B module exports a variety of functions: some are simple
utility functions, others provide a Perl program with a way to
get an initial ``handle'' on an internal object.
For descriptions of the class hierarchy of these objects and the
methods that can be called on them, see below, OVERVIEW OF CLASSES and SV-RELATED CLASSES.
Takes a reference to any Perl value, and turns the referred-to value
into an object in the appropriate B::OP-derived or B::SV-derived
class. Apart from functions such as main_root, this is the primary
way to get an initial ``handle'' on an internal perl data structure
which can then be followed with the other access methods.
The returned object will only be valid as long as the underlying OPs
and SVs continue to exist. Do not attempt to use the object after the
underlying structures are freed.
Walk the symbol table starting at SYMREF and call METHOD on each
symbol (a B::GV object) visited. When the walk reaches package
symbols (such as ``Foo::'') it invokes RECURSE, passing in the symbol
name, and only recurses into the package if that sub returns true.
PREFIX is the name of the SYMREF you're walking.
For example:
# Walk CGI's symbol table calling print_subs on each symbol.
# Recurse only into CGI::Util::
walksymtable(\%CGI::, 'print_subs', sub { $_[0] eq 'CGI::Util::' },
'CGI::');
print_subs() is a B::GV method you have declared. Also see B::GV Methods, below.
For descriptions of the class hierarchy of these objects and the
methods that can be called on them, see below, OVERVIEW OF CLASSES and OP-RELATED CLASSES.
Does a tree-walk of the syntax tree based at OP and calls METHOD on
each op it visits. Each node is visited before its children. If
walkoptree_debug (see below) has been called to turn debugging on then
the method walkoptree_debug is called on each op before METHOD is
called.
Returns the current debugging flag for walkoptree. If the optional
DEBUG argument is non-zero, it sets the debugging flag to that. See
the description of walkoptree above for what the debugging flag
does.
The C structures used by Perl's internals to hold SV and OP
information (PVIV, AV, HV, ..., OP, SVOP, UNOP, ...) are modelled on a
class hierarchy and the B module gives access to them via a true
object hierarchy. Structure fields which point to other objects
(whether types of SV or types of OP) are represented by the B
module as Perl objects of the appropriate class.
The bulk of the B module is the methods for accessing fields of
these structures.
Note that all access is read-only. You cannot modify the internals by
using this module. Also, note that the B::OP and B::SV objects created
by this module are only valid for as long as the underlying objects
exist; their creation doesn't increase the reference counts of the
underlying objects. Trying to access the fields of a freed object will
give incomprehensible results, or worse.
B::IV, B::NV, B::RV, B::PV, B::PVIV, B::PVNV, B::PVMG, B::BM, B::PVLV,
B::AV, B::HV, B::CV, B::GV, B::FM, B::IO. These classes correspond in
the obvious way to the underlying C structures of similar names. The
inheritance hierarchy mimics the underlying C ``inheritance''. For 5.9.1
and later this is:
Access methods correspond to the underlying C macros for field access,
usually with the leading ``class indication'' prefix removed (Sv, Av,
Hv, ...). The leading prefix is only left in cases where its removal
would cause a clash in method name. For example, GvREFCNT stays
as-is since its abbreviation would clash with the ``superclass'' method
REFCNT (corresponding to the C function SvREFCNT).
Returns a reference to the regular scalar corresponding to this
B::SV object. In other words, this method is the inverse operation
to the svref_2object() subroutine. This scalar and other data it points
at should be considered read-only: modifying them is neither safe nor
guaranteed to have a sensible effect.
Returns the value of the IV, interpreted as
a signed integer. This will be misleading ifFLAGS & SVf_IVisUV. Perhaps you want the
int_value method instead?
This method returns the value of the IV as an integer.
It differs from IV in that it returns the correct
value regardless of whether it's stored signed or
unsigned.
This method is the one you usually want. It constructs a
string using the length and offset information in the struct:
for ordinary scalars it will return the string that you'd see
from Perl, even if it contains null characters.
RV
Same as B::RV::RV, except that it will die()if the PV isn't
a reference.
This method is less often useful. It assumes that the string
stored in the struct is null-terminated, and disregards the
length information.
It is the appropriate method to use if you need to get the name
of a lexical variable from a padname array. Lexical variable names
are always stored with a null terminator, and the length field
(SvCUR) is overloaded for other purposes and can't be relied on here.
This method returns the name of the glob, but if the first
character of the name is a control character, then it converts
it to ^X first, so that *^G would return ``^G'' rather than ``\cG''.
It's useful if you want to print out the name of a variable.
If you restrict yourself to globs which exist at compile-time
then the result ought to be unambiguous, because code like
${"^G"} = 1 is compiled as two ops - a constant string and
a dereference (rv2gv) - so that the glob is created at runtime.
If you're working with globs at runtime, and need to disambiguate
*^G from *{``^G''}, then you should use the raw NAME method.
Takes one arguments ( 'stdin' | 'stdout' | 'stderr' ) and returns true if the IoIFP of the object is equal to the handle whose name was
passed as argument ( i.e. $io->IsSTD('stderr') is true ifIoIFP($io) == PerlIO_stdin() ).
These classes correspond in the obvious way to the underlying C
structures of similar names. The inheritance hierarchy mimics the
underlying C ``inheritance'':
