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
IVX
needs64bits
packiv

B::NV METHODS

NV
NVX

B::RV METHODS

RV

B::PV METHODS

PV

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

NAME
STASH
SV
IO
FORM
AV
HV
EGV
CV
CVGEN
LINE
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
FILEGV
DEPTH
PADLIST
OUTSIDE
XSUB
XSUBANY

B::HV METHODS

FILL
MAX
KEYS
RITER
NAME
PMROOT
ARRAY

OP-RELATED CLASSES

B::OP, B::UNOP, B::BINOP, B::LOGOP, B::CONDOP, B::LISTOP, B::PMOP, B::SVOP, B::GVOP, 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
ppaddr: This returns the function name as a string (e.g. pp_add, pp_rv2av).
desc: This returns the op description from the global C 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::CONDOP METHODS

true
false

B::LISTOP METHOD

children

B::PMOP METHODS

pmreplroot
pmreplstart
pmnext
pmregexp
pmflags
pmpermflags
precomp

B::SVOP METHOD

sv

B::GVOP METHOD

gv

B::PVOP METHOD

pv

B::LOOP METHODS

redoop
nextop
lastop

B::COP METHODS

label
stash
filegv
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.
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.
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.
byteload_fh(FILEHANDLE): Load the contents of FILEHANDLE as bytecode. See documentation for the Bytecode module in B::Backend for how to generate bytecode.

AUTHOR

Malcolm Beattie, mbeattie@sable.ox.ac.uk

DISCLAIMER

We are painfully aware that these documents may contain incorrect links and misformatted HTML. Such bugs lie in the automatic translation process that automatically created the hundreds and hundreds of separate documents that you find here. Please do not report link or formatting bugs, because we cannot fix per-document problems. The only bug reports that will help us are those that supply working patches to the installhtml or pod2html programs, or to the Pod::HTML module itself, for which I and the entire Perl community will shower you with thanks and praises.

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--Tom Christiansen, Perl Documentation Compiler and Editor

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