Data::Dump::Streamer(3User Contributed Perl DocumentatiData::Dump::Streamer(3)NAMEData::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
persistancy 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 arguements, (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 { $a->() } );
which will not be dumped correctly. Generally speaking this kind of
thing is bad practice anyway, so this should probably be viewed as a
"feature". :-)
Generally if the closures being dumped avoid accessing lexicals and
globals with the same name from out of scope and that all of the CODE
being dumped avoids vars with the "EclipseName" in their names the
dumps should be valid and should eval back into existance properly.
Note that the behaviour of dumping closures is subject to change in
future versions as its possible that I will put some additional effort
into more sophisiticated ways of avoiding name collisions in the dump.
USAGE
While Data::Dump::Streamer is at heart an object oriented module, it is
expected (based on experience with using Data::Dumper) that the common
case will not exploit these features. Nevertheless the method based
approach is convenient and accordingly a compromise hybrid approach has
been provided via the "Dump()" subroutine. Such as
Dump($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 relevent 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 doesnt. 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 relevent 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 surpress
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();
Wheras 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 mutliple times the output
will be single a list multiplier statement, and not each item output
seperately. Thus: "Dump([0,0,0,0])" will be output somthing 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 useage 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 equivelent to calling
Data::Dump::Streamer->new()
which means it returns an object reference.
If called with arguments and in scalar context it is equivelent 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 abreviations 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.
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
tedius, 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 boardly 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 occassional 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 equivelent 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 statments 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 statment and so generates
another, different, fix statement. The fifth entry 'V: $ARRAY1->[3]'
indicates that this slots holds a value (actually a reference value)
that is identical to one elsewhere, but is currently undefined. In
this case it is because the value it needs is the reference returned by
the anonymous array constructer in the fourth element ("$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 definately 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 dont 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.
perl v5.14.2 2012-04-03 Data::Dump::Streamer(3)
