B(3) Perl Programmers Reference Guide B(3)NAMEB - 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.
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 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
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 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
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) represent
ing 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 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.
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)
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 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.
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"
2001-03-18 perl v5.6.1 B(3)
