B(B) Perl Programmers Reference Guide B(B) 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. 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(g) 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(t) 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(e) Return the PP function name (e.g. "pp_add") of op num- ber OPNUM. hash(h) Returns a string in the form "0x..." representing the value of the internal hash function used by perl on string STR. cast_I32(2) 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(g) Returns a double-quote-surrounded escaped version of STR which can be used as a string in C source code. class(s) 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" perl v5.6.1 2001-03-03 B(B)