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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 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". 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
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.
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
PRIVATE
TYPE
FLAGS
OBJ
PTR
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
B::AV METHODS
FILL
MAX
OFF
ARRAY
AvFLAGS
B::CV METHODS
STASH
START
ROOT
GV
FILE
DEPTH
PADLIST
OUTSIDE
XSUB
XSUBANY
CvFLAGS
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::CVOP, 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". Access methods correspond
to the underlying C structre field names, with the leading "class
indication" prefix removed (op_).
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
pmpermflags
precomp
B::SVOP METHOD
sv
gv
B::PADOP METHOD
padix
B::PVOP METHOD
pv
B::LOOP METHODS
redoop
nextop
lastop
B::COP METHODS
label
stash
file
cop_seq
arybase
line
FUNCTIONS EXPORTED BY "B"
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.
main_cv
Return the (faked) CV corresponding to the main part of the Perl
program.
init_av
Returns the AV object (i.e. in class B::AV) representing INIT blocks.
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.
comppadlist
Returns the AV object (i.e. in class B::AV) of the global comppadlist.
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".
amagic_generation
Returns the SV object corresponding to the C variable
"amagic_generation".
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" (q.v.) 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.
walksymtable(SYMREF, METHOD, RECURSE)
Walk the symbol table starting at SYMREF and call METHOD on each symbol
visited. When the walk reached package symbols "Foo::" it invokes
RECURSE and only recurses into the package if that sub returns true.
svref_2object(SV)
Takes any Perl variable and turns it 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 a
internal perl data structure which can then be followed with the other
access methods.
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.
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.
AUTHOR
Malcolm Beattie, "mbeattie@sable.ox.ac.uk"
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Index for
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Alphabetical
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Top of
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