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 back
ends. 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" mod
ule is the methods for accessing fields of these struc
tures. Note that all access is read-only: you cannot mod
ify 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 under
lying C structures of similar names. The inheritance hier
archy mimics the underlying C "inheritance". Access meth
ods 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 abbre
viation 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_IVi sUV". 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 gener
ated 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 "
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 com
piled 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) == Per_
lIO_stdin() ).
B::AV METHODS
FILL MAX OFF ARRAY AvFLAGS
B::CV METHODS
STASH START ROOT GV FILE DEPTH PADLIST OUTSIDE 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::CVOP, B::LOOP, B::COP. These classes correspond in the obvious way to the under lying C structures of similar names. The inheritance hier archy mimics the underlying C "inheritance". Access meth ods 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 pmdynflags pmpermflags precomp pmoffet: 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 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) represent
ing INIT blocks.
begin_av: Returns the AV object (i.e. in class B::AV) represent
ing BEGIN blocks.
end_av: Returns the AV object (i.e. in class B::AV) represent
ing END 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 pro
gram.
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.
regex_padav: Only when perl was compiled with ithreads.
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 vis
ited 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, 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.
# Only recurse into CGI::Util::
walksymtable(CGI::, 'print_subs', sub { $_[0] eq

'CGI::Util::' },
'CGI::');
print_subs() is a B::GV method you have declared.
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 an 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 num
ber 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.

AUTHOR

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

docs.sk

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