table.pm

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  merge => "1"

and merge "a" to the value:

  $table->set(  merge => '1');
  $table->merge(merge => 'a');
  $val = $table->get('merge');

Result:

  $val == "1, a";




=item *

Start with a multivalued pair:

  merge => "1"
  merge => "2"

and merge "a" to the first value;

  $table->set(  merge => '1');
  $table->add(  merge => '2');
  $table->merge(merge => 'a');
  @val = $table->get('merge');

Result:

  $val[0] == "1, a";
  $val[1] == "2";

Only the first value for the same key is affected.



=item *

Have no entry and merge "a";

  $table->merge(miss => 'a');
  $val = $table->get('miss');

Result:

  $val == "a";

=back





=head2 C<overlap>

For each key/value pair in C<$table_b>, add the data to
C<$table_a>. The definition of C<$flags> explains how C<$flags> define
the overlapping method.

  $table_a->overlap($table_b, $flags);

=over 4

=item obj: C<$table_a>
( C<L<APR::Table object|docs::2.0::api::APR::Table>> )

The table to add the data to.

=item arg1: C<$table_b>
( C<L<APR::Table object|docs::2.0::api::APR::Table>> )

The table to iterate over, adding its data to table C<$table_a>

=item arg2: C<$flags> ( integer )

How to add the table to table C<$table_a>.

When C<$flags> == C<APR::Const::OVERLAP_TABLES_SET>, if another element
already exists with the same key, this will over-write the old data.

When C<$flags> == C<APR::Const::OVERLAP_TABLES_MERGE>, the key/value pair
from C<$table_b> is added, regardless of whether there is another
element with the same key in C<$table_a>.

=item ret: no return value

=item since: 2.0.00

=back

Access the constants via:

  use APR::Const -compile qw(:table);

or an explicit:

  use APR::Const -compile qw(OVERLAP_TABLES_SET OVERLAP_TABLES_MERGE);

This function is highly optimized, and uses less memory and CPU cycles
than a function that just loops through table C<$table_b> calling
other functions.

Conceptually, C<overlap()> does this:

  apr_array_header_t *barr = apr_table_elts(b);
  apr_table_entry_t *belt = (apr_table_entry_t *)barr-E<gt>elts;
  int i;
  
  for (i = 0; i < barr->nelts; ++i) {
      if (flags & APR_OVERLAP_TABLES_MERGE) {
          apr_table_mergen(a, belt[i].key, belt[i].val);
      }
      else {
          apr_table_setn(a, belt[i].key, belt[i].val);
      }
  }

Except that it is more efficient (less space and cpu-time) especially
when C<$table_b> has many elements.

Notice the assumptions on the keys and values in C<$table_b> -- they
must be in an ancestor of C<$table_a>'s pool.  In practice C<$table_b>
and C<$table_a> are usually from the same pool.

Examples:

=over

=item * C<APR::Const::OVERLAP_TABLES_SET>

Start with table C<$base>:

  foo => "one"
  foo => "two"
  bar => "beer"

and table C<$add>:

  foo => "three"

which is done by:

  use APR::Const    -compile => ':table';
  my $base = APR::Table::make($r->pool, TABLE_SIZE);
  my $add  = APR::Table::make($r->pool, TABLE_SIZE);
  
  $base->set(bar => 'beer');
  $base->set(foo => 'one');
  $base->add(foo => 'two');
  
  $add->set(foo => 'three');

Now overlap using C<APR::Const::OVERLAP_TABLES_SET>:

  $base->overlap($add, APR::Const::OVERLAP_TABLES_SET);

Now table C<$add> is unmodified and table C<$base> contains:

  foo => "three"
  bar => "beer"

The value from table C<add> has overwritten all previous values for
the same key both had (I<foo>).  This is the same as doing
C<L<overlay()|/C_overlay_>> followed by C<L<compress()|/C_compress_>>
with C<APR::Const::OVERLAP_TABLES_SET>.


=item * C<APR::Const::OVERLAP_TABLES_MERGE>

Start with table C<$base>:

  foo => "one"
  foo => "two"

and table C<$add>:

  foo => "three"
  bar => "beer"

which is done by:

  use APR::Const    -compile => ':table';
  my $base = APR::Table::make($r->pool, TABLE_SIZE);
  my $add  = APR::Table::make($r->pool, TABLE_SIZE);
  
  $base->set(foo => 'one');
  $base->add(foo => 'two');
  
  $add->set(foo => 'three');
  $add->set(bar => 'beer');

Now overlap using C<APR::Const::OVERLAP_TABLES_MERGE>:

  $base->overlap($add, APR::Const::OVERLAP_TABLES_MERGE);

Now table C<$add> is unmodified and table C<$base> contains:

  foo => "one, two, three"
  bar => "beer"

Values from both tables for the same key were merged into one
value. This is the same as doing C<L<overlay()|/C_overlay_>> followed
by C<L<compress()|/C_compress_>> with C<APR::Const::OVERLAP_TABLES_MERGE>.

=back





=head2 C<overlay>

Merge two tables into one new table. The resulting table may have more
than one value for the same key.

  $table = $table_base->overlay($table_overlay, $p);

=over 4

=item obj: C<$table_base>
( C<L<APR::Table object|docs::2.0::api::APR::Table>> )

The table to add at the end of the new table.

=item arg1: C<$table_overlay>
( C<L<APR::Table object|docs::2.0::api::APR::Table>> )

The first table to put in the new table.

=item arg2: C<$p>
( C<L<APR::Pool object|docs::2.0::api::APR::Pool>> )

The pool to use for the new table.

=item ret: C<$table>
( C<L<APR::Table object|docs::2.0::api::APR::Table>> )

A new table containing all of the data from the two passed in.

=item since: 2.0.00

=back


Examples:

=over

=item *

Start with table C<$base>:

  foo => "one"
  foo => "two"
  bar => "beer"

and table C<$add>:

  foo => "three"

which is done by:

  use APR::Const    -compile => ':table';
  my $base = APR::Table::make($r->pool, TABLE_SIZE);
  my $add  = APR::Table::make($r->pool, TABLE_SIZE);
  
  $base->set(bar => 'beer');
  $base->set(foo => 'one');
  $base->add(foo => 'two');
  
  $add->set(foo => 'three');

Now overlay using C<APR::Const::OVERLAP_TABLES_SET>:

  my $overlay = $base->overlay($add, APR::Const::OVERLAP_TABLES_SET);

That resulted in a new table C<$overlay> (tables C<add> and C<$base>
are unmodified) which contains:

  foo => "one"
  foo => "two"
  foo => "three"
  bar => "beer"

=back







=head2 C<set>

Add a key/value pair to a table, if another element already exists
with the same key, this will over-write the old data.

  $table->set($key, $val);

=over 4

=item obj: C<$table>
( C<L<APR::Table object|docs::2.0::api::APR::Table>> )

The table to add the data to.

=item arg1: C<$key> ( string )

The key to use.

=item arg2: C<$val> ( string )

The value to add.

=item ret: no return value

=item since: 2.0.00

=back

When adding data, this function makes a copy of both the key and the
value.



=head2 C<unset>

Remove data from the table.

  $table->unset($key);

=over 4

=item obj: C<$table>
( C<L<APR::Table object|docs::2.0::api::APR::Table>> )

The table to remove data from.

=item arg1: C<$key> ( string )

The key of the data being removed.

=item ret: no return value

=item since: 2.0.00

=back




=head1 TIE Interface

C<APR::Table> also implements a tied interface, so you can work with the
C<$table> object as a hash reference.

The following tied-hash function are supported: C<FETCH>, C<STORE>,
C<DELETE>, C<CLEAR>, C<EXISTS>, C<FIRSTKEY>, C<NEXTKEY> and
C<DESTROY>.

Note regarding the use of C<values()>. C<APR::Table> can hold more
than one key-value pair sharing the same key, so when using a table
through the tied interface, the first entry found with the right key
will be used, completely disregarding possible other entries with the
same key.  With Perl 5.8.0 and higher C<values()> will correctly list
values the corresponding to the list generated by C<keys()>. That
doesn't work with Perl 5.6. Therefore to portably iterate over the
key-value pairs, use C<each()> (which fully supports multivalued
keys), or C<APR::Table::do>.





=head2 C<EXISTS>

  $ret = $table->EXISTS($key);

=over 4

=item obj: C<$table>
( C<L<APR::Table object|docs::2.0::api::APR::Table>> )

=item arg1: C<$key> ( string )

=item ret: C<$ret> ( integer )

true or false

=item since: 2.0.00

=back





=head2 C<CLEAR>

  $table->CLEAR();

=over 4

=item obj: C<$table>
( C<L<APR::Table object|docs::2.0::api::APR::Table>> )

=item ret: no return value

=item since: 2.0.00

=back





=head2 C<STORE>

  $table->STORE($key, $val);

=over 4

=item obj: C<$table>
( C<L<APR::Table object|docs::2.0::api::APR::Table>> )

=item arg1: C<$key> ( string )

=item arg2: C<$val> ( string )

=item ret: no return value

=item since: 2.0.00

=back





=head2 C<DELETE>

  $table->DELETE($key);

=over 4

=item obj: C<$table>
( C<L<APR::Table object|docs::2.0::api::APR::Table>> )

=item arg1: C<$key> ( string )

=item ret: no return value

=item since: 2.0.00

=back





=head2 C<FETCH>

  $ret = $table->FETCH($key);

=over 4

=item obj: C<$table>
( C<L<APR::Table object|docs::2.0::api::APR::Table>> )

=item arg1: C<$key> ( string )

=item ret: C<$ret> ( string )

=item since: 2.0.00

=back

When iterating through the table's entries with C<each()>, C<FETCH>
will return the current value of a multivalued key.  For example:

  $table->add("a" => 1);
  $table->add("b" => 2);
  $table->add("a" => 3);
  
  ($k, $v) = each %$table; # (a, 1)
  print $table->{a};       # prints 1
  
  ($k, $v) = each %$table; # (b, 2)
  print $table->{a};       # prints 1
  
  ($k, $v) = each %$table; # (a, 3)
  print $table->{a};       # prints 3 !!!
  
  ($k, $v) = each %$table; # (undef, undef)
  print $table->{a};       # prints 1






=head1 See Also

L<mod_perl 2.0 documentation|docs::2.0::index>.




=head1 Copyright

mod_perl 2.0 and its core modules are copyrighted under
The Apache Software License, Version 2.0.




=head1 Authors

L<The mod_perl development team and numerous
contributors|about::contributors::people>.

=cut