MirOS Manual: B(3p)


ext::B::B(3p)   Perl Programmers Reference Guide    ext::B::B(3p)

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 docu-
     mentation 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

     The "B" module contains a set of utility functions for
     querying the current state of the Perl interpreter; typi-
     cally these functions return objects from the B::SV and
     B::OP classes, or their derived classes.  These classes in
     turn define methods for querying the resulting objects about
     their own internal state.

Utility Functions

     The "B" module exports a variety of functions: some are sim-
     ple utility functions, others provide a Perl program with a
     way to get an initial "handle" on an internal object.

     Functions Returning "B::SV", "B::AV", "B::HV", and "B::CV"
     objects

     For descriptions of the class hierarchy of these objects and
     the methods that can be called on them, see below, "OVERVIEW
     OF CLASSES" and "SV-RELATED CLASSES".

     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".

     svref_2object(SVREF)
         Takes a reference to any Perl value, and turns the
         referred-to value into an object in the appropriate

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         B::OP-derived or B::SV-derived class. Apart from func-
         tions such as "main_root", this is the primary way to
         get an initial "handle" on an internal perl data struc-
         ture which can then be followed with the other access
         methods.

         The returned object will only be valid as long as the
         underlying OPs and SVs continue to exist. Do not attempt
         to use the object after the underlying structures are
         freed.

     amagic_generation
         Returns the SV object corresponding to the C variable
         "amagic_generation".

     init_av
         Returns the AV object (i.e. in class B::AV) representing
         INIT blocks.

     check_av
         Returns the AV object (i.e. in class B::AV) representing
         CHECK blocks.

     begin_av
         Returns the AV object (i.e. in class B::AV) representing
         BEGIN blocks.

     end_av
         Returns the AV object (i.e. in class B::AV) representing
         END blocks.

     comppadlist
         Returns the AV object (i.e. in class B::AV) of the glo-
         bal comppadlist.

     regex_padav
         Only when perl was compiled with ithreads.

     main_cv
         Return the (faked) CV corresponding to the main part of
         the Perl program.

     Functions for Examining the Symbol Table

     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.

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         For example:

           # Walk CGI's symbol table calling print_subs on each symbol.
           # Recurse only into CGI::Util::
           walksymtable(\%CGI::, 'print_subs', sub { $_[0] eq 'CGI::Util::' },
                        'CGI::');

         print_subs() is a B::GV method you have declared. Also
         see "B::GV Methods", below.

     Functions Returning "B::OP" objects or for walking op trees

     For descriptions of the class hierarchy of these objects and
     the methods that can be called on them, see below, "OVERVIEW
     OF CLASSES" and "OP-RELATED CLASSES".

     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.

     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" (see below)
         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 "walkop-
         tree" above for what the debugging flag does.

     Miscellaneous Utility Functions

     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.

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     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.

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. Also, note that the B::OP
     and B::SV objects created by this module are only valid for
     as long as the underlying objects exist; their creation
     doesn't increase the reference counts of the underlying
     objects. Trying to access the fields of a freed object will
     give incomprehensible results, or worse.

     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 underly-
     ing C structures of similar names. The inheritance hierarchy
     mimics the underlying C "inheritance". For 5.9.1 and later
     this is:

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                                  B::SV
                                    |
                     +--------------+----------+------------+
                     |              |          |            |
                   B::PV          B::IV      B::NV        B::RV
                        \         /          /
                         \       /          /
                          B::PVIV          /
                              \           /
                               \         /
                                \       /
                                 B::PVNV
                                    |
                                    |
                                 B::PVMG
                                    |
                         +-----+----+------+-----+-----+
                         |     |    |      |     |     |
                       B::BM B::AV B::GV B::HV B::CV B::IO
                                    |            |
                                 B::PVLV         |
                                               B::FM

     For 5.9.0 and earlier, PVLV is a direct subclass of PVMG, so
     the base of this diagram is

                                |
                             B::PVMG
                                |
              +------+-----+----+------+-----+-----+
              |      |     |    |      |     |     |
           B::PVLV B::BM B::AV B::GV B::HV B::CV B::IO
                                             |
                                             |
                                           B::FM

     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
     object_2svref
         Returns a reference to the regular scalar corresponding
         to this B::SV object. In other words, this method is the
         inverse operation to the svref_2object() subroutine.

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         This scalar and other data it points at should be con-
         sidered read-only: modifying them is neither safe nor
         guaranteed to have a sensible effect.

     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 char-
         acters.

     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.

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     B::PVMG Methods

     MAGIC
     SvSTASH

     B::MAGIC Methods

     MOREMAGIC
     precomp
         Only valid on r-magic, returns the string that generated
         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 "\cG".

         It's useful if you want to print out the name of a vari-
         able. If you restrict yourself to globs which exist at
         compile-time then the result ought to be unambiguous,

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         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
     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) ==
         PerlIO_stdin() ).

     B::AV Methods

     FILL
     MAX
     OFF
     ARRAY
     ARRAYelt

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         Like "ARRAY", but takes an index as an argument to get
         only one element, rather than a list of all of them.

     AvFLAGS

     B::CV Methods

     STASH
     START
     ROOT
     GV
     FILE
     DEPTH
     PADLIST
     OUTSIDE
     OUTSIDE_SEQ
     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::LOOP",
     "B::COP".

     These classes correspond in the obvious way to the underly-
     ing C structures of similar names. The inheritance hierarchy
     mimics the underlying C "inheritance":

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                                      B::OP
                                        |
                        +---------------+--------+--------+
                        |               |        |        |
                     B::UNOP          B::SVOP B::PADOP  B::COP
                      ,'  `-.
                     /       `--.
                B::BINOP     B::LOGOP
                    |
                    |
                B::LISTOP
                  ,' `.
                 /     \
             B::LOOP B::PMOP

     Access methods correspond to the underlying C structre field
     names, with the leading "class indication" prefix ("op_")
     removed.

     B::OP Methods

     These methods get the values of similarly named fields
     within the OP data structure.  See top of "op.h" for more
     info.

     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
     opt
     static
     flags
     private
     spare

     B::UNOP METHOD

     first

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     B::BINOP METHOD

     last

     B::LOGOP METHOD

     other

     B::LISTOP METHOD

     children

     B::PMOP Methods

     pmreplroot
     pmreplstart
     pmnext
     pmregexp
     pmflags
     pmdynflags
     pmpermflags
     precomp
     pmoffset
         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
     stashpv
     file
     cop_seq
     arybase

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     line
     warnings
     io

AUTHOR

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

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