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B(3)
NAME
B - The Perl Compiler
SYNOPSIS
use B;
DESCRIPTION
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.
OVERVIEW
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.
Utility Functions
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.
Functions Returning "B::SV", "B::AV", "B::HV", and "B::CV" objects
For descriptions of the class hierachy of these objects and the methods
that can be called on them, see below, "OVERVIEW OF CLASSES" and
"SV-RELATED CLASSES".
sv_undef
Returns the SV object corresponding to the C variable "sv_undef".
sv_yes
Returns the SV object corresponding to the C variable "sv_yes".
sv_no
Returns the SV object corresponding to the C variable "sv_no".
svref_2object(SVREF)
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.
amagic_generation
Returns the SV object corresponding to the C variable
"amagic_generation".
init_av
Returns the AV object (i.e. in class B::AV) representing INIT blocks.
check_av
Returns the AV object (i.e. in class B::AV) representing CHECK blocks.
begin_av
Returns the AV object (i.e. in class B::AV) representing BEGIN blocks.
end_av
Returns the AV object (i.e. in class B::AV) representing END blocks.
comppadlist
Returns the AV object (i.e. in class B::AV) of the global comppadlist.
regex_padav
Only when perl was compiled with ithreads.
main_cv
Return the (faked) CV corresponding to the main part of the Perl
program.
Functions for Examining the Symbol Table
walksymtable(SYMREF, METHOD, RECURSE, PREFIX)
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.
Functions Returning "B::OP" objects or for walking op trees
For descriptions of the class hierachy of these objects and the methods
that can be called on them, see below, "OVERVIEW OF CLASSES" and
"OP-RELATED CLASSES".
main_root
Returns the root op (i.e. an object in the appropriate B::OP-derived
class) of the main part of the Perl program.
main_start
Returns the starting op of the main part of the Perl program.
walkoptree(OP, METHOD)
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.
walkoptree_debug(DEBUG)
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.
Miscellaneous Utility Functions
ppname(OPNUM)
Return the PP function name (e.g. "pp_add") of op number OPNUM.
hash(STR)
Returns a string in the form "0x..." representing the value of the
internal hash function used by perl on string STR.
cast_I32(I)
Casts I to the internal I32 type used by that perl.
minus_c
Does the equivalent of the "-c" command-line option. Obviously, this is
only useful in a BEGIN block or else the flag is set too late.
cstring(STR)
Returns a double-quote-surrounded escaped version of STR which can be
used as a string in C source code.
perlstring(STR)
Returns a double-quote-surrounded escaped version of STR which can be
used as a string in Perl source code.
class(OBJ)
Returns the class of an object without the part of the classname
preceding the first "::". This is used to turn "B::UNOP" into "UNOP"
for example.
threadsv_names
In a perl compiled for threads, this returns a list of the special
per-thread threadsv variables.
OVERVIEW OF CLASSES
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.
SV-RELATED CLASSES
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":
B::SV
|
+--------------+----------------------+
| | |
B::PV B::IV B::RV
| \ / \
| \ / \
| B::PVIV B::NV
\ /
\____ __/
\ /
B::PVNV
|
|
B::PVMG
|
+------+-----+----+------+-----+-----+
| | | | | | |
B::PVLV B::BM B::AV B::GV B::HV B::CV B::IO
|
|
B::FM
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").
B::SV Methods
REFCNT
FLAGS
object_2svref
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.
B::IV Methods
IV Returns the value of the IV, interpreted as a signed integer. This will
be misleading if "FLAGS & SVf_IVisUV". Perhaps you want the "int_value"
method instead?
IVX
UVX
int_value
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.
needs64bits
packiv
B::NV Methods
NV
NVX
B::RV Methods
RV
B::PV Methods
PV 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.
PVX 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.
B::PVMG Methods
MAGIC
SvSTASH
B::MAGIC Methods
MOREMAGIC
precomp
Only valid on r-magic, returns the string that generated the regexp.
PRIVATE
TYPE
FLAGS
OBJ Will die() if called on r-magic.
PTR
REGEX
Only valid on r-magic, returns the integer value of the REGEX stored in
the MAGIC.
B::PVLV Methods
TARGOFF
TARGLEN
TYPE
TARG
B::BM Methods
USEFUL
PREVIOUS
RARE
TABLE
B::GV Methods
is_empty
This method returns TRUE if the GP field of the GV is NULL.
NAME
SAFENAME
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.
STASH
SV
IO
FORM
AV
HV
EGV
CV
CVGEN
LINE
FILE
FILEGV
GvREFCNT
FLAGS
B::IO Methods
LINES
PAGE
PAGE_LEN
LINES_LEFT
TOP_NAME
TOP_GV
FMT_NAME
FMT_GV
BOTTOM_NAME
BOTTOM_GV
SUBPROCESS
IoTYPE
IoFLAGS
IsSTD
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. $io->IsSTD('stderr') is true if IoIFP($io) ==
PerlIO_stdin() ).
B::AV Methods
FILL
MAX
OFF
ARRAY
ARRAYelt
Like "ARRAY", but takes an index as an argument to get only one
element, rather than a list of all of them.
AvFLAGS
B::CV Methods
STASH
START
ROOT
GV
FILE
DEPTH
PADLIST
OUTSIDE
OUTSIDE_SEQ
XSUB
XSUBANY
For constant subroutines, returns the constant SV returned by the
subroutine.
CvFLAGS
const_sv
B::HV Methods
FILL
MAX
KEYS
RITER
NAME
PMROOT
ARRAY
OP-RELATED CLASSES
"B::OP", "B::UNOP", "B::BINOP", "B::LOGOP", "B::LISTOP", "B::PMOP",
"B::SVOP", "B::PADOP", "B::PVOP", "B::LOOP", "B::COP".
These classes correspond in the obvious way to the underlying C structures
of similar names. The inheritance hierarchy mimics the underlying C
"inheritance":
B::OP
|
+---------------+--------+--------+
| | | |
B::UNOP B::SVOP B::PADOP B::COP
,' `-.
/ `--.
B::BINOP B::LOGOP
|
|
B::LISTOP
,' `.
/ \
B::LOOP B::PMOP
Access methods correspond to the underlying C structre field names, with
the leading "class indication" prefix ("op_") removed.
B::OP Methods
next
sibling
name
This returns the op name as a string (e.g. "add", "rv2av").
ppaddr
This returns the function name as a string (e.g. "PL_ppaddr[OP_ADD]",
"PL_ppaddr[OP_RV2AV]").
desc
This returns the op description from the global C PL_op_desc array
(e.g. "addition" "array deref").
targ
type
seq
flags
private
B::UNOP METHOD
first
B::BINOP METHOD
last
B::LOGOP METHOD
other
B::LISTOP METHOD
children
B::PMOP Methods
pmreplroot
pmreplstart
pmnext
pmregexp
pmflags
pmdynflags
pmpermflags
precomp
pmoffset
Only when perl was compiled with ithreads.
B::SVOP METHOD
sv
gv
B::PADOP METHOD
padix
B::PVOP METHOD
pv
B::LOOP Methods
redoop
nextop
lastop
B::COP Methods
label
stash
stashpv
file
cop_seq
arybase
line
warnings
io
AUTHOR
Malcolm Beattie, "mbeattie@sable.ox.ac.uk"
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Index for
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