opcode.3

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.\" ========================================================================
.\"
.IX Title "Opcode 3"
.TH Opcode 3 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Opcode \- Disable named opcodes when compiling perl code
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&  use Opcode;
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Perl code is always compiled into an internal format before execution.
.PP
Evaluating perl code (e.g. via \*(L"eval\*(R" or \*(L"do 'file'\*(R") causes
the code to be compiled into an internal format and then,
provided there was no error in the compilation, executed.
The internal format is based on many distinct \fIopcodes\fR.
.PP
By default no opmask is in effect and any code can be compiled.
.PP
The Opcode module allow you to define an \fIoperator mask\fR to be in
effect when perl \fInext\fR compiles any code.  Attempting to compile code
which contains a masked opcode will cause the compilation to fail
with an error. The code will not be executed.
.SH "NOTE"
.IX Header "NOTE"
The Opcode module is not usually used directly. See the ops pragma and
Safe modules for more typical uses.
.SH "WARNING"
.IX Header "WARNING"
The authors make \fBno warranty\fR, implied or otherwise, about the
suitability of this software for safety or security purposes.
.PP
The authors shall not in any case be liable for special, incidental,
consequential, indirect or other similar damages arising from the use
of this software.
.PP
Your mileage will vary. If in any doubt \fBdo not use it\fR.
.SH "Operator Names and Operator Lists"
.IX Header "Operator Names and Operator Lists"
The canonical list of operator names is the contents of the array
PL_op_name defined and initialised in file \fIopcode.h\fR of the Perl
source distribution (and installed into the perl library).
.PP
Each operator has both a terse name (its opname) and a more verbose or
recognisable descriptive name. The opdesc function can be used to
return a list of descriptions for a list of operators.
.PP
Many of the functions and methods listed below take a list of
operators as parameters. Most operator lists can be made up of several
types of element. Each element can be one of
.IP "an operator name (opname)" 8
.IX Item "an operator name (opname)"
Operator names are typically small lowercase words like enterloop,
leaveloop, last, next, redo etc. Sometimes they are rather cryptic
like gv2cv, i_ncmp and ftsvtx.
.IP "an operator tag name (optag)" 8
.IX Item "an operator tag name (optag)"
Operator tags can be used to refer to groups (or sets) of operators.
Tag names always begin with a colon. The Opcode module defines several
optags and the user can define others using the define_optag function.
.IP "a negated opname or optag" 8
.IX Item "a negated opname or optag"
An opname or optag can be prefixed with an exclamation mark, e.g., !mkdir.
Negating an opname or optag means remove the corresponding ops from the
accumulated set of ops at that point.
.IP "an operator set (opset)" 8
.IX Item "an operator set (opset)"
An \fIopset\fR as a binary string of approximately 44 bytes which holds a
set or zero or more operators.
.Sp
The opset and opset_to_ops functions can be used to convert from
a list of operators to an opset and \fIvice versa\fR.
.Sp
Wherever a list of operators can be given you can use one or more opsets.
See also Manipulating Opsets below.
.SH "Opcode Functions"
.IX Header "Opcode Functions"
The Opcode package contains functions for manipulating operator names
tags and sets. All are available for export by the package.
.IP "opcodes" 8
.IX Item "opcodes"
In a scalar context opcodes returns the number of opcodes in this
version of perl (around 350 for perl\-5.7.0).
.Sp
In a list context it returns a list of all the operator names.
(Not yet implemented, use \f(CW@names\fR = opset_to_ops(full_opset).)
.IP "opset (\s-1OP\s0, ...)" 8
.IX Item "opset (OP, ...)"
Returns an opset containing the listed operators.
.IP "opset_to_ops (\s-1OPSET\s0)" 8
.IX Item "opset_to_ops (OPSET)"
Returns a list of operator names corresponding to those operators in
the set.
.IP "opset_to_hex (\s-1OPSET\s0)" 8
.IX Item "opset_to_hex (OPSET)"
Returns a string representation of an opset. Can be handy for debugging.
.IP "full_opset" 8
.IX Item "full_opset"
Returns an opset which includes all operators.
.IP "empty_opset" 8
.IX Item "empty_opset"
Returns an opset which contains no operators.
.IP "invert_opset (\s-1OPSET\s0)" 8
.IX Item "invert_opset (OPSET)"
Returns an opset which is the inverse set of the one supplied.
.IP "verify_opset (\s-1OPSET\s0, ...)" 8
.IX Item "verify_opset (OPSET, ...)"
Returns true if the supplied opset looks like a valid opset (is the
right length etc) otherwise it returns false. If an optional second
parameter is true then verify_opset will croak on an invalid opset
instead of returning false.
.Sp
Most of the other Opcode functions call verify_opset automatically
and will croak if given an invalid opset.
.IP "define_optag (\s-1OPTAG\s0, \s-1OPSET\s0)" 8
.IX Item "define_optag (OPTAG, OPSET)"
Define \s-1OPTAG\s0 as a symbolic name for \s-1OPSET\s0. Optag names always start
with a colon \f(CW\*(C`:\*(C'\fR.
.Sp
The optag name used must not be defined already (define_optag will
croak if it is already defined). Optag names are global to the perl
process and optag definitions cannot be altered or deleted once
defined.
.Sp
It is strongly recommended that applications using Opcode should use a
leading capital letter on their tag names since lowercase names are
reserved for use by the Opcode module. If using Opcode within a module
you should prefix your tags names with the name of your module to
ensure uniqueness and thus avoid clashes with other modules.
.IP "opmask_add (\s-1OPSET\s0)" 8
.IX Item "opmask_add (OPSET)"
Adds the supplied opset to the current opmask. Note that there is
currently \fIno\fR mechanism for unmasking ops once they have been masked.
This is intentional.
.IP "opmask" 8
.IX Item "opmask"
Returns an opset corresponding to the current opmask.
.IP "opdesc (\s-1OP\s0, ...)" 8
.IX Item "opdesc (OP, ...)"
This takes a list of operator names and returns the corresponding list
of operator descriptions.
.IP "opdump (\s-1PAT\s0)" 8
.IX Item "opdump (PAT)"
Dumps to \s-1STDOUT\s0 a two column list of op names and op descriptions.
If an optional pattern is given then only lines which match the
(case insensitive) pattern will be output.
.Sp
It's designed to be used as a handy command line utility:
.Sp
.Vb 2
\&        perl \-MOpcode=opdump \-e opdump
\&        perl \-MOpcode=opdump \-e \*(Aqopdump Eval\*(Aq
.Ve
.SH "Manipulating Opsets"
.IX Header "Manipulating Opsets"
Opsets may be manipulated using the perl bit vector operators & (and), | (or),
^ (xor) and ~ (negate/invert).
.PP
However you should never rely on the numerical position of any opcode
within the opset. In other words both sides of a bit vector operator
should be opsets returned from Opcode functions.
.PP
Also, since the number of opcodes in your current version of perl might
not be an exact multiple of eight, there may be unused bits in the last
byte of an upset. This should not cause any problems (Opcode functions
ignore those extra bits) but it does mean that using the ~ operator
will typically not produce the same 'physical' opset 'string' as the
invert_opset function.
.SH "TO DO (maybe)"
.IX Header "TO DO (maybe)"
.Vb 1
\&    $bool = opset_eq($opset1, $opset2)  true if opsets are logically eqiv