Provided by: libdata-dump-streamer-perl_2.41-1_amd64 
NAME
Data::Dump::Streamer - Accurately serialize a data structure as Perl code.
SYNOPSIS
use Data::Dump::Streamer;
use DDS; # optionally installed alias
Dump($x,$y); # Prints to STDOUT
Dump($x,$y)->Out(); # " "
my $o=Data::Dump::Streamer->new(); # Returns a new ...
my $o=Dump(); # ... uninitialized object.
my $o=Dump($x,$y); # Returns an initialized object
my $s=Dump($x,$y)->Out(); # " a string of the dumped obj
my @l=Dump($x,$y); # " a list of code fragments
my @l=Dump($x,$y)->Out(); # " a list of code fragments
Dump($x,$y)->To(\*STDERR)->Out(); # Prints to STDERR
Dump($x,$y)->Names('foo','bar') # Specify Names
->Out();
Dump($x,$y)->Indent(0)->Out(); # No indent
Dump($x,$y)->To(\*STDERR) # Output to STDERR
->Indent(0) # ... no indent
->Names('foo','bar') # ... specify Names
->Out(); # Print...
$o->Data($x,$y); # OO form of what Dump($x,$y) does.
$o->Names('Foo','Names'); # ...
$o->Out(); # ...
DESCRIPTION
Given a list of scalars or reference variables, writes out their contents in perl syntax.
The references can also be objects. The contents of each variable is output using the
least number of Perl statements as convenient, usually only one. Self-referential
structures, closures, and objects are output correctly.
The return value can be evaled to get back an identical copy of the original reference
structure. In some cases this may require the use of utility subs that
Data::Dump::Streamer will optionally export.
This module is very similar in concept to the core module Data::Dumper, with the major
differences being that this module is designed to output to a stream instead of
constructing its output in memory (trading speed for memory), and that the traversal over
the data structure is effectively breadth first versus the depth first traversal done by
the others.
In fact the data structure is scanned twice, first in breadth first mode to perform
structural analysis, and then in depth first mode to actually produce the output, but
obeying the depth relationships of the first pass.
Caveats Dumping Closures (CODE Refs)
As of version 1.11 DDS has had the ability to dump closures properly. This means that the
lexicals that are bound to the closure are dumped along with the subroutine that uses
them. This makes it much easier to debug code that uses closures and to a certain extent
provides a persistency framework for closure based code. The way this works is that DDS
figures out what all the lexicals are that are bound to CODE refs it is dumping and then
pretends that it had originally been called with all of them as its arguments, (along with
the original arguments as well of course.)
One consequence of the way the dumping process works is that all of the recreated
subroutines will be in the same scope. This of course can lead to collisions as two
subroutines can easily be bound to different variables that have the same name.
The way that DDS resolves these collisions is that it renames one of the variables with a
special name so that presumably there are no collisions. However this process is very
simplistic with no checks to prevent collisions with other lexicals or other globals that
may be used by other dumped code. In some situations it may be necessary to change the
default value of the rename template which may be done by using the "EclipseName" method.
Similarly to the problem of colliding lexicals is the problem of colliding lexicals and
globals. DDS pays no attention to globals when dumping closures which can potentially
result in lexicals being declared that will eclipse their global namesake. There is
currently no way around this other than to avoid accessing a global and a lexical with the
same name from the subs being dumped. An example is
my $a = sub { $a++ };
Dump( sub { $a->() } );
which will not be dumped correctly. Generally speaking this kind of thing is bad practice
anyway, so this should probably be viewed as a "feature". :-)
Generally if the closures being dumped avoid accessing lexicals and globals with the same
name from out of scope and that all of the CODE being dumped avoids vars with the
"EclipseName" in their names the dumps should be valid and should eval back into existence
properly.
Note that the behaviour of dumping closures is subject to change in future versions as its
possible that I will put some additional effort into more sophisticated ways of avoiding
name collisions in the dump.
USAGE
While Data::Dump::Streamer is at heart an object oriented module, it is expected (based on
experience with using Data::Dumper) that the common case will not exploit these features.
Nevertheless the method based approach is convenient and accordingly a compromise hybrid
approach has been provided via the "Dump()" subroutine. Such as
Dump($foo);
$as_string= Dump($foo)->Out();
All attribute methods are designed to be chained together. This means that when used as
set attribute (called with arguments) they return the object they were called against.
When used as get attributes (called without arguments) they return the value of the
attribute.
From an OO point of view the key methods are the "Data()" and "Out()" methods. These
correspond to the breadth first and depth first traversal, and need to be called in this
order. Some attributes must be set prior to the "Data()" phase and some need only be set
before the "Out()" phase.
Attributes once set last the lifetime of the object, unless explicitly reset.
Controlling Object Representation
This module provides hooks to allow objects to override how they are represented. The
basic idea is that a subroutine (or method) is provided which is responsible for the
override. The return of the method governs how the object will be represented when dumped,
and how it will be restored. The basic calling convention is
my ( $proxy, $thaw, $postop )= $callback->($obj);
#or = $obj->$method();
The "Freezer()" method controls what methods to use as a default method and also allows
per class overrides. When dumping an object of a given class the first time it tries to
execute the class specific handler if it is specified, then the user specific generic
handler if its been specified and then "DDS_freeze". This means that class authors can
implement a "DDS_freeze()" method and their objects will automatically be serialized as
necessary. Note that if either the class specific or generic handler is defined but false
"DDS_freeze()" will not be used even if it is present.
The interface of the "Freezer()" handler in detail is as follows:
$obj
The object being dumped.
$proxy
This is what will be dumped instead of $obj. It may be one of the following values:
"undef" (first time only)
On the first time a serialization hook is called in a dump it may return undef
or the empty list to indicate that it shouldn't be used again for this class
during this pass. Any other time undef is treated the same as false.
FALSE value
A false value for $proxy is taken to mean that it should be ignored. Its like
saying IgnoreClass(ref($obj)); Note that undef has a special meaning when the
callback is called the first time.
A Reference
A reference that will be dumped instead of the object.
Perl Code
A string that is to be treated as code and inserted directly into the dump
stream as a proxy for the original. Note that the code must be able to execute
inline or in other words must evaluate to a perl EXPR. Use "do{}" to wrap
multistatement code.
$thaw
This values is used to allow extra control over how the object will be recreated when
dumped. It is used for converting the $proxy representation into the real thing. It is
only relevant when $proxy is a reference.
FALSE value
Indicates no thaw action is to be included for this object.
Sub or Method Name
A string matching "/^(->)?((?:\w*::)\w+)(\(\))?$/" in which case it is taken
as a sub name when the string ends in () and a method name when the string
doesn't. If the "->" is present then the sub or method is called inline. If it
is not then the sub or method is called after the main dump.
Perl Code
Any other string, in which case the result will be taken as code which will be
emitted after the main dump. It will be wrapped in a for loop that aliases $_
to the variable in question.
$postdump
This is the similar to $thaw but is called in process instead of being emitted as part
of the dump. Any return is ignored. It is only relevant when $proxy is a reference.
FALSE value
No postdump action is to occur.
Code Reference
The code ref will be called after serialization is complete with the object as
the argument.
Method Name
The method will be called after serialization is complete
An example DDS_freeze method is one I had to put together for an object which contained a
key whose value was a ref to an array tied to the value of another key. Dumping this got
crazy, so I wanted to suppress dumping the tied array. I did it this way:
sub DDS_freeze {
my $self=shift;
delete $self->{'tie'};
return ($self,'->fix_tie','fix_tie');
}
sub fix_tie {
my $self=shift;
if ( ! $self->{'tie'} ) {
$self->{str}="" unless defined $self->{str};
tie my @a, 'Tie::Array::PackedC', $self->{str};
$self->{'tie'} = \@a;
}
return $self;
}
The $postop means the object is relatively unaffected after the dump, the $thaw says that
we should also include the method inline as we dump. An example dump of an object like
this might be
$Foo1=bless({ str=>'' },'Foo')->fix_tie();
Whereas if we omit the "->" then we would get:
$Foo1=bless({ str=>'' },'Foo');
$Foo1->fix_tie();
In our example it wouldn't actually make a difference, but the former style can be nicer
to read if the object is embedded in another. However the non arrow notation is slightly
more dangerous, in that its possible that the internals of the object will not be fully
linked when the method is evaluated. The second form guarantees that the object will be
fully linked when the method is evaluated.
See "Controlling Hash Traversal and Display Order" for a different way to control the
representation of hash based objects.
Controlling Hash Traversal and Display Order
When dumping a hash you may control the order the keys will be output and which keys will
be included. The basic idea is to specify a subroutine which takes a hash as an argument
and returns a reference to an array containing the keys to be dumped.
You can use the KeyOrder() routine or the SortKeys() routine to specify the sorter to be
used.
The routine will be called in the following way:
( $key_array, $thaw ) = $sorter->($hash,($pass=0),$addr,$class);
( $key_array,) = $sorter->($hash,($pass=1),$addr,$class);
$hash is the hash to be dumped, $addr is the refaddr() of the $hash, and $class will be
set if the hash has been blessed.
When $pass is 0 the $thaw variable may be supplied as well as the keyorder. If it is
defined then it specifies what thaw action to perform after dumping the hash. See $thaw in
"Controlling Object Representation" for details as to how it works. This allows an object
to define those keys needed to recreate itself properly, and a followup hook to recreate
the rest.
Note that if a Freezer() method is defined and returns a $thaw then the $thaw returned by
the sorter will override it.
Controlling Array Presentation and Run Length Encoding
By default Data::Dump::Streamer will "run length encode" array values. This means that
when an array value is simple (ie, its not referenced and does contain a reference) and is
repeated multiple times the output will be single a list multiplier statement, and not
each item output separately. Thus: "Dump([0,0,0,0])" will be output something like
$ARRAY1 = [ (0) x 4 ];
This is particularly useful when dealing with large arrays that are only partly filled,
and when accidentally the array has been made very large, such as with the improper use of
pseudo-hash notation.
To disable this feature you may set the Rle() property to FALSE, by default it is enabled
and set to TRUE.
Installing DDS as a package alias
Its possible to have an alias to Data::Dump::Streamer created and installed for easier
usage in one liners and short scripts. Data::Dump::Streamer is a bit long to type
sometimes. However because this technically means polluting the root level namespace, and
having it listed on CPAN, I have elected to have the installer not install it by default.
If you wish it to be installed you must explicitly state so when Build.Pl is run:
perl Build.Pl DDS [Other Module::Build options]
Then a normal './Build test, ./Build install' invocation will install DDS.
Using DDS is identical to Data::Dump::Streamer.
use-time package aliasing
You can also specify an alias at use-time, then use that alias in the rest of your
program, thus avoiding the permanent (but modest) namespace pollution of the previous
method.
use Data::Dumper::Streamer as => 'DDS';
# or if you prefer
use Data::Dumper::Streamer;
import Data::Dumper::Streamer as => 'DDS';
You can use any alias you like, but that doesn't mean you should.. Folks doing as => 'DBI'
will be mercilessly ridiculed.
PadWalker support
If PadWalker 1.0 is installed you can use DumpLex() to try to automatically determine the
names of the vars being dumped. As long as the vars being dumped have my or our
declarations in scope the vars will be correctly named. Padwalker will also be used
instead of the B:: modules when dumping closures when it is available.
INTERFACE
Data::Dumper Compatibility
For drop in compatibility with the Dumper() usage of Data::Dumper, you may request that
the Dumper() method is exported. It will not be exported by default. In addition the
standard Data::Dumper::Dumper() may be exported on request as "DDumper". If you provide
the tag ":Dumper" then both will be exported.
Dumper
Dumper LIST
A synonym for scalar Dump(LIST)->Out for usage compatibility with Data::Dumper
DDumper
DDumper LIST
A secondary export of the actual Data::Dumper::Dumper subroutine.
Constructors
new Creates a new Data::Dump::Streamer object. Currently takes no arguments and simply
returns the new object with a default style configuration.
See "Dump()" for a better way to do things.
Dump
Dump VALUES
Smart non method based constructor.
This routine behaves very differently depending on the context it is called in and
whether arguments are provided.
If called with no arguments it is exactly equivalent to calling
Data::Dump::Streamer->new()
which means it returns an object reference.
If called with arguments and in scalar context it is equivalent to calling
Data::Dump::Streamer->new()->Data(@vals)
except that the actual depth first traversal is delayed until "Out()" is called. This
means that options that must be provided before the "Data()" phase can be provided
after the call to "Dump()". Again, it returns a object reference.
If called with arguments and in void or list context it is equivelent to calling
Data::Dump::Streamer->new()->Data(@vals)->Out()
The reason this is true in list context is to make "print Dump(...),"\n";" do the
right thing. And also that combined with method chaining options can be added or
removed as required quite easily and naturally.
So to put it short:
my $obj=Dump($x,$y); # Returns an object
my $str=Dump($x,$y)->Out(); # Returns a string of the dump.
my @code=Dump($x,$y); # Returns a list of the dump.
Dump($x,$y); # prints the dump.
print Dump($x,$y); # prints the dump.
It should be noted that the setting of "$\" will affect the behaviour of both of
Dump($x,$y);
print Dump($x,$y);
but it will not affect the behaviour of
print scalar Dump($x,$y);
Note As of 1.11 Dump also works as a method, with identical properties as when called
as a subroutine, with the exception that when called with no arguments it is a synonym
for "Out()". Thus
$obj->Dump($foo)->Names('foo')->Out();
will work fine, as will the odd looking:
$obj->Dump($foo)->Names('foo')->Dump();
which are both the same as
$obj->Names('foo')->Data($foo)->Out();
Hopefully this should make method use more or less DWIM.
DumpLex VALUES
DumpLex is similar to Dump except it will try to automatically determine the names to
use for the variables being dumped by using PadWalker to have a poke around the
calling lexical scope to see what is declared. If a name for a var can't be found then
it will be named according to the normal scheme. When PadWalker isn't installed this
is just a wrapper for Dump().
Thanks to Ovid for the idea of this. See Data::Dumper::Simple for a similar wrapper
around Data::Dumper.
DumpVars PAIRS
This is wrapper around Dump() which expect to receive a list of name=>value pairs
instead of a list of values. Otherwise behaves like Dump(). Note that names starting
with a '-' are treated the same as those starting with '*' when passed to Names().
Methods
Data
Data LIST
Analyzes a list of variables in breadth first order.
If called with arguments then the internal object state is reset before scanning the
list of arguments provided.
If called with no arguments then whatever arguments were provided to "Dump()" will be
scanned.
Returns $self.
Out
Out VALUES
Prints out a set of values to the appropriate location. If provided a list of values
then the values are first scanned with "Data()" and then printed, if called with no
values then whatever was scanned last with "Data()" or "Dump()" is printed.
If the "To()" attribute was provided then will dump to whatever object was specified
there (any object, including filehandles that accept the print() method), and will
always return $self.
If the "To()" attribute was not provided then will use an internal printing object,
returning either a list or scalar or printing to STDOUT in void context.
This routine is virtually always called without arguments as the last method in the
method chain.
Dump->Arguments(1)->Out(@vars);
$obj->Data(@vars)->Out();
Dump(@vars)->Out;
Data::Dump::Streamer->Out(@vars);
All should DWIM.
Names
Names LIST
Names ARRAYREF
Takes a list of strings or a reference to an array of strings to use for var names for
the objects dumped. The names may be prefixed by a * indicating the variable is to be
dumped as its dereferenced type if it is an array, hash or code ref. Otherwise the
star is ignored. Other sigils may be prefixed but they will be silently converted to
*'s.
If no names are provided then names are generated automatically based on the type of
object being dumped, with abbreviations applied to compound class names.
If called with arguments then returns the object itself, otherwise in list context
returns the list of names in use, or in scalar context a reference or undef. In void
context with no arguments the names are cleared.
NOTE: Must be called before "Data()" is called.
If you wish to have no names, use Terse.
Terse
Terse BOOL
When true, no variable names will be created. Data will be dumped as anonymous
references or values.
Dump([])->Out; # $ARRAY1 = []
Dump([])->Terse(1)->Out; # []
Purity
Purity BOOL
This option can be used to set the level of purity in the output. It defaults to TRUE,
which results in the module doing its best to ensure that the resulting dump when
eval()ed is precisely the same as the input. However, at times such as debugging this
can be tedious, resulting in extremely long dumps with many "fix" statements involved.
By setting Purity to FALSE the resulting output won't necessarily be legal Perl, but
it will be more legible. In this mode the output is broadly similar to that of the
default setting of Data::Dumper (Purity(0)). When set to TRUE the behaviour is
likewise similar to Data::Dumper in Purity(1) but more accurate.
When Purity() is set to FALSE aliases will be output with a function call wrapper of
'alias_to' whose argument will be the value the item is an alias to. This wrapper does
nothing, and is only there as a visual cue. Likewise, 'make_ro' will be output when
the value was readonly, and again the effect is cosmetic only.
To
To STREAMER
Specifies the object to print to. Data::Dump::Streamer can stream its output to any
object supporting the print method. This is primarily meant for streaming to a
filehandle, however any object that supports the method will do.
If a filehandle is specified then it is used until it is explicitly changed, or the
object is destroyed.
Declare
Declare BOOL
If Declare is True then each object is dumped with 'my' declarations included, and all
rules that follow are obeyed. (Ie, not referencing an undeclared variable). If Declare
is False then all objects are expected to be previously defined and references to top
level objects can be made at any time.
Defaults to False.
Indent
Indent INT
If Indent is True then data is output in an indented and fairly neat fashion. If the
value is 2 then hash key/value pairs and array values each on their own line. If the
value is 1 then a "smart" indenting mode is activated where multiple key/value or
values may be printed to the same line. The heuristics for this mode are still
experimental so it may occasional not indent very nicely.
Default is Indent(2)
If indent is False then no indentation is done, and all optional whitespace. is
omitted. See <OptSpace()|/OptSpace> for more details.
Defaults to True.
Newlines are appended to each statement regardless of this value.
Indentkeys
Indentkeys BOOL
If Indent() and Indentkeys are True then hashes with more than one key value pair are
dumped such that the keys and values line up. Note however this means each key has to
be quoted twice. Not advised for very large data structures. Additional logic may
enhance this feature soon.
Defaults to True.
NOTE: Must be set before "Data()" is called.
OptSpace
OptSpace STR
Normally DDS emits a lot of whitespace in between tokens that it emits. Using this
method you can control how much whitespace it will emit, or even if some other string
should be used.
If Indent is set to 0 then this value is automatically set to the empty string. When
Indent is set back to a non zero value the old value will be restored if it has not
been changed from the empty string in the intervening time.
KeyOrder TYPE_OR_OBJ
KeyOrder TYPE_OR_OBJ, VALUE
Sets or returns the key order to for use for a given type or object.
TYPE_OR_OBJ may be a string representing a class, or "" for representing unblessed
objects, or it maybe a reference to a hash.
VALUE may be a string representing one of built in sort mechanisms, or it may be a
reference to a subroutine, or a method name if TYPE_OR_OBJ is not an object.
The built in sort mechanisms are 'aphabetical'/'lexical', 'numeric',
'smart'/'intelligent' and 'each'.
If VALUE is omitted returns the current value for the given type.
If TYPE_OR_OBJ is omitted or FALSE it defaults to "" which represents unblessed
hashes.
See "Controlling Hash Traversal and Display Order" for more details.
SortKeys
SortKeys VALUE
This is a wrapper for KeyOrder. It allows only the generic hash sort order to be
specified a little more elegantly than via KeyOrder(). It is syntactically equivalent
to
$self->KeyOrder( "", @_ );
Verbose
Verbose BOOL
If Verbose is True then when references that cannot be resolved in a single statement
are encountered the reference is substituted for a descriptive tag saying what type of
forward reference it is, and to what is being referenced. The type is provided through
a prefix, "R:" for reference, and "A:" for alias, "V:" for a value and then the name
of the var in a string. Automatically generated var names are also reduced to the
shortest possible unique abbreviation, with some tricks thrown in for
Long::Class::Names::Like::This (which would abbreviate most likely to LCNLT1)
If Verbose if False then a simple placeholder saying 'A' or 'R' is provided. (In most
situations perl requires a placeholder, and as such one is always provided, even if
technically it could be omitted.)
This setting does not change the followup statements that fix up the structure, and
does not result in a loss of accuracy, it just makes it a little harder to read. OTOH,
it means dumps can be quite a bit smaller and less noisy.
Defaults to True.
NOTE: Must be set before "Data()" is called.
DumpGlob
DumpGlob BOOL
If True then globs will be followed and fully defined, otherwise the globs will still
be referenced but their current value will not be set.
Defaults to True
NOTE: Must be set before "Data()" is called.
Deparse
Deparse BOOL
If True then CODE refs will be deparsed use B::Deparse and included in the dump. If it
is False the a stub subroutine reference will be output as per the setting of
"CodeStub()".
Caveat Emptor, dumping subroutine references is hardly a secure act, and it is
provided here only for convenience.
Note using this routine is at your own risk as of DDS 1.11, how it interacts with the
newer advanced closure dumping process is undefined.
EclipseName
EclipseName SPRINTF_FORMAT
When necessary DDS will rename vars output during deparsing with this value. It is a
sprintf format string that should contain only and both of the "%s" and a "%d" formats
in any order along with whatever other literal text you want in the name. No checks
are performed on the validity of this value so be careful. It defaults to
"%s_eclipse_%d"
where the "%s" represents the name of the var being eclipsed, and the "%d" a counter
to ensure all such mappings are unique.
DeparseOpts
DeparseOpts LIST
DeparseOpts ARRAY
If Deparse is True then these options will be passed to B::Deparse->new() when dumping
a CODE ref. If passed a list of scalars the list is used as the arguments. If passed
an array reference then this array is assumed to contain a list of arguments. If no
arguments are provided returns a an array ref of arguments in scalar context, and a
list of arguments in list context.
Note using this routine is at your own risk as of DDS 1.11, how it interacts with the
newer advanced closure dumping process is undefined.
CodeStub
CodeStub STRING
If Deparse is False then this string will be used in place of CODE references. Its the
users responsibility to make sure its compilable and blessable.
Defaults to 'sub { Carp::confess "Dumped code stub!" }'
FormatStub
FormatStub STRING
If Deparse is False then this string will be used in place of FORMAT references. Its
the users responsibility to make sure its compilable and blessable.
Defaults to 'do{ local *F; eval "format F =\nFormat Stub\n.\n"; *F{FORMAT} }'
DeparseGlob
DeparseGlob BOOL
If Deparse is TRUE then this style attribute will determine if subroutines and
FORMAT's contained in globs that are dumped will be deparsed or not.
Defaults to True.
Dualvars
Dualvars BOOL
Dualvars
Dualvars BOOL
If TRUE then dualvar checking will occur and the required statements emitted to
recreate dualvars when they are encountered, otherwise items will be dumped in their
stringified form always. It defaults to TRUE.
Rle
Rle BOOL
RLE
RLE BOOL
If True then arrays will be run length encoded using the "x" operator. What this
means is that if an array contains repeated elements then instead of outputting each
and every one a list multiplier will be output. This means that considerably less
space is taken to dump redundant data.
Freezer
Freezer ACTION
Freezer CLASS, ACTION
This method can be used to override the DDS_freeze hook for a specific class. If CLASS
is omitted then the ACTION applies to all blessed object.
If ACTION is false it indicates that the given CLASS should not have any serilization
hooks called.
If ACTION is a string then it is taken to be the method name that will be executed to
freeze the object. CLASS->can(METHOD) must return true or the setting will be ignored.
If ACTION is a code ref it is executed with the object as the argument.
When called with no arguments returns in scalar context the generic serialization
method (defaults to 'DDS_freeze'), in list context returns the generic serialization
method followed by a list of pairs of Classname=>ACTION.
If the action executes a sub or method it is expected to return a list of three
values:
( $proxy, $thaw, $postdump )=$obj->DDS_Freeze();
See "Controlling Object Representation" for more details.
NOTE: Must be set before "Data()" is called.
Ignore
Ignore OBJ_OR_CLASS
Ignore OBJ_OR_CLASS, BOOL
Allows a given object or class to be ignored, and replaced with a string containing
the name of the item ignored.
If called with no args returns a list of items ignored (using the refaddr to represent
objects). If called with a single argument returns whether that argument is ignored.
If called with more than one arguments then expects a list of pairs of object =>
is_ignored.
Returns $self when setting.
NOTE: Must be set before "Data()" is called.
Compress
Compress SIZE
Controls compression of string values (not keys). If this value is nonzero and a
string to be dumped is longer than its value then the Compressor() if defined is used
to compress the string. Setting size to -1 will cause all strings to be processed,
setting size to 0 will cause no strings to be processed.
Compressor
Compressor CODE
This attribute is used to control the compression of strings. It is expected to be a
reference to a subroutine with the following interface:
my $prelude_code=$compressor->(); # no arguments.
my $code=$compressor->('string'); # string argument
The sub will be called with no arguments at the beginning of the dump to allow any
require statements or similar to be added. During the dump the sub will be called with
a single argument when compression is required. The code returned in this case is
expected to be an EXPR that will evaluate back to the original string.
By default DDS will use Compress::Zlib in conjunction with MIME::Base64 to do
compression and encoding, and exposes the 'usqz' subroutine for handling the decoding
and decompression.
The abbreviated name was chosen as when using the default compressor every string will
be represented by a string like
usqz('....')
Meaning that eight characters are required without considering the data itself.
Likewise Base64 was chosen because it is a representation that is high-bit safe,
compact and easy to quote. Escaped strings are much less efficient for storing binary
data.
Reading the Output
As mentioned in Verbose there is a notation used to make understanding the output easier.
However at first glance it can probably be a bit confusing. Take the following example:
my $x=1;
my $y=[];
my $array=sub{\@_ }->( $x,$x,$y );
push @$array,$y,1;
unshift @$array,\$array->[-1];
Dump($array);
Which prints (without the comments of course):
$ARRAY1 = [
'R: $ARRAY1->[5]', # resolved by fix 1
1,
'A: $ARRAY1->[1]', # resolved by fix 2
[],
'V: $ARRAY1->[3]', # resolved by fix 3
1
];
$ARRAY1->[0] = \$ARRAY1->[5]; # fix 1
alias_av(@$ARRAY1, 2, $ARRAY1->[1]); # fix 2
$ARRAY1->[4] = $ARRAY1->[3]; # fix 3
The first entry, 'R: $ARRAY1->[5]' indicates that this slot in the array holds a reference
to the currently undefined "$ARRAY1->[5]", and as such the value will have to be provided
later in what the author calls 'fix' statements. The third entry 'A: $ARRAY1->[1]'
indicates that is element of the array is in fact the exact same scalar as exists in
"$ARRAY1->[1]", or is in other words, an alias to that variable. Again, this cannot be
expressed in a single statement and so generates another, different, fix statement. The
fifth entry 'V: $ARRAY1->[3]' indicates that this slots holds a value (actually a
reference value) that is identical to one elsewhere, but is currently undefined. In this
case it is because the value it needs is the reference returned by the anonymous array
constructor in the fourth element ("$ARRAY1->[3]"). Again this results in yet another
different fix statement. If Verbose() is off then only a 'R' 'A' or 'V' tag is emitted as
a marker of some form is necessary.
All of this specialized behaviour can be bypassed by setting Purity() to FALSE, in which
case the output will look very similar to what Data::Dumper outputs in low Purity setting.
In a later version I'll try to expand this section with more examples.
A Note About Speed
Data::Dumper is much faster than this module for many things. However IMO it is less
readable, and definitely less accurate. YMMV.
EXPORT
By default exports the Dump() command. Or may export on request the same command as
Stream(). A Data::Dumper::Dumper compatibility routine is provided via requesting Dumper
and access to the real Data::Dumper::Dumper routine is provided via DDumper. The later two
are exported together with the :Dumper tag.
Additionally there are a set of internally used routines that are exposed. These are
mostly direct copies of routines from Array::RefElem, Lexical::Alias and Scalar::Util,
however some where marked have had their semantics slightly changed, returning defined but
false instead of undef for negative checks, or throwing errors on failure.
The following XS subs (and tagnames for various groupings) are exportable on request.
:Dumper
Dumper
DDumper
:undump # Collection of routines needed to undump something
alias_av # aliases a given array value to a scalar
alias_hv # aliases a given hashes value to a scalar
alias_ref # aliases a scalar to another scalar
make_ro # makes a scalar read only
lock_keys # pass through to Hash::Util::lock_keys
lock_keys_plus # like lock_keys, but adds keys to those present
lock_ref_keys # like lock_keys but operates on a hashref
lock_ref_keys_plus # like lock_keys_plus but operates on a hashref
dualvar # make a variable with different string/numeric
# representation
alias_to # pretend to return an alias, used in low
# purity mode to indicate a value is actually
# an alias to something else.
:alias # all croak on failure
alias_av(@Array,$index,$var);
alias_hv(%hash,$key,$var);
alias_ref(\$var1,\$var2);
push_alias(@array,$var);
:util
blessed($var) #undef or a class name.
isweak($var) #returns true if $var contains a weakref
reftype($var) #the underlying type or false but defined.
refaddr($var) #a references address
refcount($var) #the number of times a reference is referenced
sv_refcount($var) #the number of times a scalar is referenced.
weak_refcount($var) #the number of weakrefs to an object.
#sv_refcount($var)-weak_refcount($var) is the true
#SvREFCOUNT() of the var.
looks_like_number($var) #if perl will think this is a number.
regex($var) # In list context returns the pattern and the modifiers,
# in scalar context returns the pattern in (?msix:) form.
# If not a regex returns false.
readonly($var) # returns whether the $var is readonly
weaken($var) # cause the reference contained in var to become weak.
make_ro($var) # causes $var to become readonly, returns the value of $var.
reftype_or_glob # returns the reftype of a reference, or if its not
# a reference but a glob then the globs name
refaddr_or_glob # similar to reftype_or_glob but returns an address
# in the case of a reference.
globname # returns an evalable string to represent a glob, or
# the empty string if not a glob.
:all # (Dump() and Stream() and Dumper() and DDumper()
# and all of the XS)
:bin # (not Dump() but all of the rest of the XS)
By default exports only Dump(), DumpLex() and DumpVars(). Tags are provided for exporting
'all' subroutines, as well as 'bin' (not Dump()), 'util' (only introspection utilities)
and 'alias' for the aliasing utilities. If you need to ensure that you can eval the
results (undump) then use the 'undump' tag.
BUGS
Code with this many debug statements is certain to have errors. :-)
Please report them with as much of the error output as possible.
Be aware that to a certain extent this module is subject to whimsies of your local perl.
The same code may not produce the same dump on two different installs and versions.
Luckily these don't seem to pop up often.
AUTHOR AND COPYRIGHT
Yves Orton, yves at cpan org.
Copyright (C) 2003-2005 Yves Orton
This library is free software; you can redistribute it and/or modify it under the same
terms as Perl itself.
Contains code derived from works by Gisle Aas, Graham Barr, Jeff Pinyan, Richard Clamp,
and Gurusamy Sarathy.
Thanks to Dan Brook, Yitzchak Scott-Thoennes, eric256, Joshua ben Jore, Jim Cromie, Curtis
"Ovid" Poe, Lars DXXXXXX, and anybody that I've forgotten for patches, feedback and ideas.
SEE ALSO (its a crowded space, isn't it!)
Data::Dumper - the mother of them all
Data::Dumper::Simple - Auto named vars with source filter interface.
Data::Dumper::Names - Auto named vars without source filtering.
Data::Dumper::EasyOO - easy to use wrapper for DD
Data::Dump - Has cool feature to squeeze data
Data::Dump::Streamer - The best perl dumper. But I would say that. :-)
Data::TreeDumper - Non perl output, lots of rendering options
And of course www.perlmonks.org and perl itself.