| B - The Perl Compiler |
B
B - The Perl Compiler
use B;
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.
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.
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).
FLAGS & SVf_IVisUV. Perhaps you want the
int_value method instead?
IV in that it returns the correct
value regardless of whether it's stored signed or
unsigned.
die() if the PV isn't
a reference.
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.
die() if called on r-magic.
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
${"^G"} = 1 is compiled as two ops - a constant string and
a dereference (rv2gv) - so that the glob is created at runtime.
If you're working with globs at runtime, and need to disambiguate *^G from *{``^G''}, then you should use the raw NAME method.
IsSTD('stderr') is true if
IoIFP($io) == PerlIO_stdin() ).
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_).
BThe 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.
sv_undef.
sv_yes.
sv_no.
amagic_generation.
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)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.
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)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)hash(STR)cast_I32(I)-c command-line option. Obviously, this
is only useful in a BEGIN block or else the flag is set too late.
cstring(STR)perlstring(STR)class(OBJ)
Malcolm Beattie, mbeattie@sable.ox.ac.uk
| B - The Perl Compiler |