ScalarArray.pm   [plain text]

package IO::ScalarArray;


=head1 NAME

IO::ScalarArray - IO:: interface for reading/writing an array of scalars


=head1 SYNOPSIS

Perform I/O on strings, using the basic OO interface...

    use IO::ScalarArray;
    @data = ("My mes", "sage:\n");

    ### Open a handle on an array, and append to it:
    $AH = new IO::ScalarArray \@data;
    $AH->print("Hello");       
    $AH->print(", world!\nBye now!\n");  
    print "The array is now: ", @data, "\n";

    ### Open a handle on an array, read it line-by-line, then close it:
    $AH = new IO::ScalarArray \@data;
    while (defined($_ = $AH->getline)) { 
	print "Got line: $_";
    }
    $AH->close;

    ### Open a handle on an array, and slurp in all the lines:
    $AH = new IO::ScalarArray \@data;
    print "All lines:\n", $AH->getlines; 

    ### Get the current position (either of two ways):
    $pos = $AH->getpos;         
    $offset = $AH->tell;  

    ### Set the current position (either of two ways):
    $AH->setpos($pos);        
    $AH->seek($offset, 0);

    ### Open an anonymous temporary array:
    $AH = new IO::ScalarArray;
    $AH->print("Hi there!");
    print "I printed: ", @{$AH->aref}, "\n";      ### get at value


Don't like OO for your I/O?  No problem.  
Thanks to the magic of an invisible tie(), the following now 
works out of the box, just as it does with IO::Handle:
    
    use IO::ScalarArray;
    @data = ("My mes", "sage:\n");

    ### Open a handle on an array, and append to it:
    $AH = new IO::ScalarArray \@data;
    print $AH "Hello";    
    print $AH ", world!\nBye now!\n";
    print "The array is now: ", @data, "\n";

    ### Open a handle on a string, read it line-by-line, then close it:
    $AH = new IO::ScalarArray \@data;
    while (<$AH>) {
	print "Got line: $_";
    }
    close $AH;

    ### Open a handle on a string, and slurp in all the lines:
    $AH = new IO::ScalarArray \@data;
    print "All lines:\n", <$AH>;

    ### Get the current position (WARNING: requires 5.6):
    $offset = tell $AH;

    ### Set the current position (WARNING: requires 5.6):
    seek $AH, $offset, 0;

    ### Open an anonymous temporary scalar:
    $AH = new IO::ScalarArray;
    print $AH "Hi there!";
    print "I printed: ", @{$AH->aref}, "\n";      ### get at value


And for you folks with 1.x code out there: the old tie() style still works,
though this is I<unnecessary and deprecated>:

    use IO::ScalarArray;

    ### Writing to a scalar...
    my @a; 
    tie *OUT, 'IO::ScalarArray', \@a;
    print OUT "line 1\nline 2\n", "line 3\n";
    print "Array is now: ", @a, "\n"

    ### Reading and writing an anonymous scalar... 
    tie *OUT, 'IO::ScalarArray';
    print OUT "line 1\nline 2\n", "line 3\n";
    tied(OUT)->seek(0,0);
    while (<OUT>) { 
        print "Got line: ", $_;
    }



=head1 DESCRIPTION

This class is part of the IO::Stringy distribution;
see L<IO::Stringy> for change log and general information.

The IO::ScalarArray class implements objects which behave just like 
IO::Handle (or FileHandle) objects, except that you may use them 
to write to (or read from) arrays of scalars.  Logically, an
array of scalars defines an in-core "file" whose contents are
the concatenation of the scalars in the array.  The handles created by 
this class are automatically tiehandle'd (though please see L<"WARNINGS">
for information relevant to your Perl version).

For writing large amounts of data with individual print() statements, 
this class is likely to be more efficient than IO::Scalar.

Basically, this:

    my @a;
    $AH = new IO::ScalarArray \@a;
    $AH->print("Hel", "lo, ");         ### OO style
    $AH->print("world!\n");            ### ditto

Or this:

    my @a;
    $AH = new IO::ScalarArray \@a;
    print $AH "Hel", "lo, ";           ### non-OO style
    print $AH "world!\n";              ### ditto

Causes @a to be set to the following array of 3 strings:

    ( "Hel" , 
      "lo, " , 
      "world!\n" )

See L<IO::Scalar> and compare with this class.


=head1 PUBLIC INTERFACE

=cut

use Carp;
use strict;
use vars qw($VERSION @ISA);
use IO::Handle;

# The package version, both in 1.23 style *and* usable by MakeMaker:
$VERSION = substr q$Revision: 1.1 $, 10;

# Inheritance:
@ISA = qw(IO::Handle);
require IO::WrapTie and push @ISA, 'IO::WrapTie::Slave' if ($] >= 5.004);


#==============================

=head2 Construction 

=over 4

=cut

#------------------------------

=item new [ARGS...]

I<Class method.>
Return a new, unattached array handle.  
If any arguments are given, they're sent to open().

=cut

sub new {
    my $proto = shift;
    my $class = ref($proto) || $proto;
    my $self = bless \do { local *FH }, $class;
    tie *$self, $class, $self;
    $self->open(@_);  ### open on anonymous by default
    $self;
}
sub DESTROY { 
    shift->close;
}


#------------------------------

=item open [ARRAYREF]

I<Instance method.>
Open the array handle on a new array, pointed to by ARRAYREF.
If no ARRAYREF is given, a "private" array is created to hold
the file data.

Returns the self object on success, undefined on error.

=cut

sub open {
    my ($self, $aref) = @_;

    ### Sanity:
    defined($aref) or do {my @a; $aref = \@a};
    (ref($aref) eq "ARRAY") or croak "open needs a ref to a array";

    ### Setup:
    $self->setpos([0,0]);
    *$self->{AR} = $aref;
    $self;
}

#------------------------------

=item opened

I<Instance method.>
Is the array handle opened on something?

=cut

sub opened {
    *{shift()}->{AR};
}

#------------------------------

=item close

I<Instance method.>
Disassociate the array handle from its underlying array.
Done automatically on destroy.

=cut

sub close {
    my $self = shift;
    %{*$self} = ();
    1;
}

=back

=cut



#==============================

=head2 Input and output

=over 4

=cut

#------------------------------

=item flush 

I<Instance method.>
No-op, provided for OO compatibility.

=cut

sub flush {} 

#------------------------------

=item getc

I<Instance method.>
Return the next character, or undef if none remain.
This does a read(1), which is somewhat costly.

=cut

sub getc {
    my $buf = '';
    ($_[0]->read($buf, 1) ? $buf : undef);
}

#------------------------------

=item getline

I<Instance method.>
Return the next line, or undef on end of data.
Can safely be called in an array context.
Currently, lines are delimited by "\n".

=cut

sub getline {
    my $self = shift;
    my ($str, $line) = (undef, '');


    ### Minimal impact implementation!
    ### We do the fast fast thing (no regexps) if using the
    ### classic input record separator.

    ### Case 1: $/ is undef: slurp all...    
    if    (!defined($/)) {

	### Get the rest of the current string, followed by remaining strings:
	my $ar = *$self->{AR};
	my @slurp = (
		     substr($ar->[*$self->{Str}], *$self->{Pos}),
		     @$ar[(1 + *$self->{Str}) .. $#$ar ] 
		     );
	     	
	### Seek to end:
	$self->_setpos_to_eof;
	return join('', @slurp);
    }

    ### Case 2: $/ is "\n": 
    elsif ($/ eq "\012") {    
	
	### Until we hit EOF (or exitted because of a found line):
	until ($self->eof) {
	    ### If at end of current string, go fwd to next one (won't be EOF):
	    if ($self->_eos) {++*$self->{Str}, *$self->{Pos}=0};

	    ### Get ref to current string in array, and set internal pos mark:
	    $str = \(*$self->{AR}[*$self->{Str}]); ### get current string
	    pos($$str) = *$self->{Pos};            ### start matching from here
	
	    ### Get from here to either \n or end of string, and add to line:
	    $$str =~ m/\G(.*?)((\n)|\Z)/g;         ### match to 1st \n or EOS
	    $line .= $1.$2;                        ### add it
	    *$self->{Pos} += length($1.$2);        ### move fwd by len matched
	    return $line if $3;                    ### done, got line with "\n"
        }
        return ($line eq '') ? undef : $line;  ### return undef if EOF
    }

    ### Case 3: $/ is ref to int.  Bail out.
    elsif (ref($/)) {
        croak '$/ given as a ref to int; currently unsupported';
    }

    ### Case 4: $/ is either "" (paragraphs) or something weird...
    ###         Bail for now.
    else {                
        croak '$/ as given is currently unsupported';
    }
}

#------------------------------

=item getlines

I<Instance method.>
Get all remaining lines.
It will croak() if accidentally called in a scalar context.

=cut

sub getlines {
    my $self = shift;
    wantarray or croak("can't call getlines in scalar context!");
    my ($line, @lines);
    push @lines, $line while (defined($line = $self->getline));
    @lines;
}

#------------------------------

=item print ARGS...

I<Instance method.>
Print ARGS to the underlying array.  

Currently, this always causes a "seek to the end of the array"
and generates a new array entry.  This may change in the future.

=cut

sub print {
    my $self = shift;
    push @{*$self->{AR}}, join('', @_);      ### add the data
    $self->_setpos_to_eof;
    1;
}

#------------------------------

=item read BUF, NBYTES, [OFFSET];

I<Instance method.>
Read some bytes from the array.
Returns the number of bytes actually read, 0 on end-of-file, undef on error.

=cut

sub read {
    my $self = $_[0];
    ### we must use $_[1] as a ref
    my $n    = $_[2];
    my $off  = $_[3] || 0;

    ### print "getline\n";
    my $justread;
    my $len;
    ($off ? substr($_[1], $off) : $_[1]) = '';

    ### Stop when we have zero bytes to go, or when we hit EOF:
    my @got;
    until (!$n or $self->eof) {       
        ### If at end of current string, go forward to next one (won't be EOF):
        if ($self->_eos) {
            ++*$self->{Str};
            *$self->{Pos} = 0;
        }

        ### Get longest possible desired substring of current string:
        $justread = substr(*$self->{AR}[*$self->{Str}], *$self->{Pos}, $n);
        $len = length($justread);
        push @got, $justread;
        $n            -= $len; 
        *$self->{Pos} += $len;
    }
    $_[1] .= join('', @got);
    return length($_[1])-$off;
}

#------------------------------

=item write BUF, NBYTES, [OFFSET];

I<Instance method.>
Write some bytes into the array.

=cut

sub write {
    my $self = $_[0];
    my $n    = $_[2];
    my $off  = $_[3] || 0;

    my $data = substr($_[1], $n, $off);
    $n = length($data);
    $self->print($data);
    return $n;
}


=back

=cut



#==============================

=head2 Seeking/telling and other attributes

=over 4

=cut

#------------------------------

=item autoflush 

I<Instance method.>
No-op, provided for OO compatibility.

=cut

sub autoflush {} 

#------------------------------

=item binmode

I<Instance method.>
No-op, provided for OO compatibility.

=cut

sub binmode {} 

#------------------------------

=item clearerr

I<Instance method.>  Clear the error and EOF flags.  A no-op.

=cut

sub clearerr { 1 }

#------------------------------

=item eof 

I<Instance method.>  Are we at end of file?

=cut

sub eof {
    ### print "checking EOF [*$self->{Str}, *$self->{Pos}]\n";
    ### print "SR = ", $#{*$self->{AR}}, "\n";

    return 0 if (*{$_[0]}->{Str} < $#{*{$_[0]}->{AR}});  ### before EOA
    return 1 if (*{$_[0]}->{Str} > $#{*{$_[0]}->{AR}});  ### after EOA
    ###                                                  ### at EOA, past EOS:
    ((*{$_[0]}->{Str} == $#{*{$_[0]}->{AR}}) && ($_[0]->_eos)); 
}

#------------------------------
#
# _eos
#
# I<Instance method, private.>  Are we at end of the CURRENT string?
#
sub _eos {
    (*{$_[0]}->{Pos} >= length(*{$_[0]}->{AR}[*{$_[0]}->{Str}])); ### past last char
}

#------------------------------

=item seek POS,WHENCE

I<Instance method.>
Seek to a given position in the stream.
Only a WHENCE of 0 (SEEK_SET) is supported.

=cut

sub seek {
    my ($self, $pos, $whence) = @_; 

    ### Seek:
    if    ($whence == 0) { $self->_seek_set($pos); }
    elsif ($whence == 1) { $self->_seek_cur($pos); }
    elsif ($whence == 2) { $self->_seek_end($pos); }
    else                 { croak "bad seek whence ($whence)" }
}

#------------------------------
#
# _seek_set POS
#
# Instance method, private.
# Seek to $pos relative to start:
#
sub _seek_set {
    my ($self, $pos) = @_; 

    ### Advance through array until done:
    my $istr = 0;
    while (($pos >= 0) && ($istr < scalar(@{*$self->{AR}}))) {
	if (length(*$self->{AR}[$istr]) > $pos) {   ### it's in this string! 
	    return $self->setpos([$istr, $pos]);
	}
	else {                                      ### it's in next string
	    $pos -= length(*$self->{AR}[$istr++]);  ### move forward one string
	}
    }
    ### If we reached this point, pos is at or past end; zoom to EOF:
    return $self->_setpos_to_eof;
}

#------------------------------
#
# _seek_cur POS
#
# Instance method, private.
# Seek to $pos relative to current position.
#
sub _seek_cur {
    my ($self, $pos) = @_; 
    $self->_seek_set($self->tell + $pos);
}

#------------------------------
#
# _seek_end POS
#
# Instance method, private.
# Seek to $pos relative to end.
# We actually seek relative to beginning, which is simple.
#
sub _seek_end {
    my ($self, $pos) = @_; 
    $self->_seek_set($self->_tell_eof + $pos);
}

#------------------------------

=item tell

I<Instance method.>
Return the current position in the stream, as a numeric offset.

=cut

sub tell {
    my $self = shift;
    my $off = 0;
    my ($s, $str_s);
    for ($s = 0; $s < *$self->{Str}; $s++) {   ### count all "whole" scalars
	defined($str_s = *$self->{AR}[$s]) or $str_s = '';
	###print STDERR "COUNTING STRING $s (". length($str_s) . ")\n";
	$off += length($str_s);
    }
    ###print STDERR "COUNTING POS ($self->{Pos})\n";
    return ($off += *$self->{Pos});            ### plus the final, partial one
}

#------------------------------
#
# _tell_eof
#
# Instance method, private.
# Get position of EOF, as a numeric offset.
# This is identical to the size of the stream - 1.
#
sub _tell_eof {
    my $self = shift;
    my $len = 0;
    foreach (@{*$self->{AR}}) { $len += length($_) }
    $len;
}

#------------------------------

=item setpos POS

I<Instance method.>
Seek to a given position in the array, using the opaque getpos() value.
Don't expect this to be a number.

=cut

sub setpos { 
    my ($self, $pos) = @_;
    (ref($pos) eq 'ARRAY') or
	die "setpos: only use a value returned by getpos!\n";
    (*$self->{Str}, *$self->{Pos}) = @$pos;
}

#------------------------------
#
# _setpos_to_eof
#
# Fast-forward to EOF.
#
sub _setpos_to_eof {
    my $self = shift;
    $self->setpos([scalar(@{*$self->{AR}}), 0]);
}

#------------------------------

=item getpos

I<Instance method.>
Return the current position in the array, as an opaque value.
Don't expect this to be a number.

=cut

sub getpos {
    [*{$_[0]}->{Str}, *{$_[0]}->{Pos}];
}

#------------------------------

=item aref

I<Instance method.>
Return a reference to the underlying array.

=cut

sub aref {
    *{shift()}->{AR};
}

=back

=cut

#------------------------------
# Tied handle methods...
#------------------------------

### Conventional tiehandle interface:
sub TIEHANDLE { (defined($_[1]) && UNIVERSAL::isa($_[1],"IO::ScalarArray"))
		    ? $_[1] 
		    : shift->new(@_) }
sub GETC      { shift->getc(@_) }
sub PRINT     { shift->print(@_) }
sub PRINTF    { shift->print(sprintf(shift, @_)) }
sub READ      { shift->read(@_) }
sub READLINE  { wantarray ? shift->getlines(@_) : shift->getline(@_) }
sub WRITE     { shift->write(@_); }
sub CLOSE     { shift->close(@_); }
sub SEEK      { shift->seek(@_); }
sub TELL      { shift->tell(@_); }
sub EOF       { shift->eof(@_); }

#------------------------------------------------------------

1;
__END__

# SOME PRIVATE NOTES:
#
#     * The "current position" is the position before the next
#       character to be read/written.
#
#     * Str gives the string index of the current position, 0-based
#
#     * Pos gives the offset within AR[Str], 0-based.
#
#     * Inital pos is [0,0].  After print("Hello"), it is [1,0].



=head1 WARNINGS

Perl's TIEHANDLE spec was incomplete prior to 5.005_57;
it was missing support for C<seek()>, C<tell()>, and C<eof()>.
Attempting to use these functions with an IO::ScalarArray will not work
prior to 5.005_57. IO::ScalarArray will not have the relevant methods 
invoked; and even worse, this kind of bug can lie dormant for a while.
If you turn warnings on (via C<$^W> or C<perl -w>),
and you see something like this...

    attempt to seek on unopened filehandle

...then you are probably trying to use one of these functions
on an IO::ScalarArray with an old Perl.  The remedy is to simply
use the OO version; e.g.:

    $AH->seek(0,0);    ### GOOD: will work on any 5.005
    seek($AH,0,0);     ### WARNING: will only work on 5.005_57 and beyond



=head1 VERSION

$Id: ScalarArray.pm,v 1.1 2004/04/09 17:04:45 dasenbro Exp $


=head1 AUTHOR

=head2 Principal author

Eryq (F<eryq@zeegee.com>).
President, ZeeGee Software Inc (F<http://www.zeegee.com>).


=head2 Other contributors 

Thanks to the following individuals for their invaluable contributions
(if I've forgotten or misspelled your name, please email me!):

I<Andy Glew,>
for suggesting C<getc()>.

I<Brandon Browning,>
for suggesting C<opened()>.

I<Eric L. Brine,>
for his offset-using read() and write() implementations. 

I<Doug Wilson,>
for the IO::Handle inheritance and automatic tie-ing.

=cut

#------------------------------
1;