our @ISA = qw(Exporter);
our @EXPORT_OK = qw(
all any first min max minstr maxstr none notall product reduce sum sum0 shuffle
- pairmap pairgrep pairfirst pairs pairkeys pairvalues
+ pairs unpairs pairkeys pairvalues pairmap pairgrep pairfirst
);
-our $VERSION = "1.39";
+our $VERSION = "1.42_01";
our $XS_VERSION = $VERSION;
$VERSION = eval $VERSION;
The remaining list-reduction functions are all specialisations of this generic
idea.
-=head2 $b = any { BLOCK } @list
+=head2 any
+
+ my $bool = any { BLOCK } @list;
I<Since version 1.33.>
# at least one string has more than 10 characters
}
-=head2 $b = all { BLOCK } @list
+=head2 all
+
+ my $bool = all { BLOCK } @list;
I<Since version 1.33.>
-Similar to C<any>, except that it requires all elements of the C<@list> to make
-the C<BLOCK> return true. If any element returns false, then it returns false.
-If the C<BLOCK> never returns false or the C<@list> was empty then it returns
-true.
+Similar to L</any>, except that it requires all elements of the C<@list> to
+make the C<BLOCK> return true. If any element returns false, then it returns
+false. If the C<BLOCK> never returns false or the C<@list> was empty then it
+returns true.
+
+=head2 none
+
+=head2 notall
-=head2 $b = none { BLOCK } @list
+ my $bool = none { BLOCK } @list;
-=head2 $b = notall { BLOCK } @list
+ my $bool = notall { BLOCK } @list;
I<Since version 1.33.>
-Similar to C<any> and C<all>, but with the return sense inverted. C<none>
-returns true only if no value in the LIST causes the BLOCK to return true, and
-C<notall> returns true only if not all of the values do.
+Similar to L</any> and L</all>, but with the return sense inverted. C<none>
+returns true only if no value in the C<@list> causes the C<BLOCK> to return
+true, and C<notall> returns true only if not all of the values do.
-=head2 $val = first { BLOCK } @list
+=head2 first
+
+ my $val = first { BLOCK } @list;
Similar to C<grep> in that it evaluates C<BLOCK> setting C<$_> to each element
of C<@list> in turn. C<first> returns the first element where the result from
$foo = first { $_ > $value } @list # first value in @list which
# is greater than $value
-=head2 $num = max @list
+=head2 max
+
+ my $num = max @list;
Returns the entry in the list with the highest numerical value. If the list is
empty then C<undef> is returned.
$foo = max 3,9,12 # 12
$foo = max @bar, @baz # whatever
-=head2 $str = maxstr @list
+=head2 maxstr
-Similar to C<max>, but treats all the entries in the list as strings and
+ my $str = maxstr @list;
+
+Similar to L</max>, but treats all the entries in the list as strings and
returns the highest string as defined by the C<gt> operator. If the list is
empty then C<undef> is returned.
$foo = maxstr "hello","world" # "world"
$foo = maxstr @bar, @baz # whatever
-=head2 $num = min @list
+=head2 min
+
+ my $num = min @list;
-Similar to C<max> but returns the entry in the list with the lowest numerical
+Similar to L</max> but returns the entry in the list with the lowest numerical
value. If the list is empty then C<undef> is returned.
$foo = min 1..10 # 1
$foo = min 3,9,12 # 3
$foo = min @bar, @baz # whatever
-=head2 $str = minstr @list
+=head2 minstr
-Similar to C<min>, but treats all the entries in the list as strings and
+ my $str = minstr @list;
+
+Similar to L</min>, but treats all the entries in the list as strings and
returns the lowest string as defined by the C<lt> operator. If the list is
empty then C<undef> is returned.
$foo = minstr "hello","world" # "hello"
$foo = minstr @bar, @baz # whatever
-=head2 $num = product @list
+=head2 product
+
+ my $num = product @list;
I<Since version 1.35.>
$foo = product 1..10 # 3628800
$foo = product 3,9,12 # 324
-=head2 $num_or_undef = sum @list
+=head2 sum
+
+ my $num_or_undef = sum @list;
Returns the numerical sum of all the elements in C<@list>. For backwards
compatibility, if C<@list> is empty then C<undef> is returned.
$foo = sum 3,9,12 # 24
$foo = sum @bar, @baz # whatever
-=head2 $num = sum0 @list
+=head2 sum0
+
+ my $num = sum0 @list;
I<Since version 1.26.>
-Similar to C<sum>, except this returns 0 when given an empty list, rather than
-C<undef>.
+Similar to L</sum>, except this returns 0 when given an empty list, rather
+than C<undef>.
=cut
of the pairs, and will not be confused by multiple pairs having the same "key"
value - nor even do they require that the first of each pair be a plain string.
+B<NOTE>: At the time of writing, the following C<pair*> functions that take a
+block do not modify the value of C<$_> within the block, and instead operate
+using the C<$a> and C<$b> globals instead. This has turned out to be a poor
+design, as it precludes the ability to provide a C<pairsort> function. Better
+would be to pass pair-like objects as 2-element array references in C<$_>, in
+a style similar to the return value of the C<pairs> function. At some future
+version this behaviour may be added.
+
+Until then, users are alerted B<NOT> to rely on the value of C<$_> remaining
+unmodified between the outside and the inside of the control block. In
+particular, the following example is B<UNSAFE>:
+
+ my @kvlist = ...
+
+ foreach (qw( some keys here )) {
+ my @items = pairgrep { $a eq $_ } @kvlist;
+ ...
+ }
+
+Instead, write this using a lexical variable:
+
+ foreach my $key (qw( some keys here )) {
+ my @items = pairgrep { $a eq $key } @kvlist;
+ ...
+ }
+
=cut
-=head2 @kvlist = pairgrep { BLOCK } @kvlist
+=head2 pairs
+
+ my @pairs = pairs @kvlist;
+
+I<Since version 1.29.>
+
+A convenient shortcut to operating on even-sized lists of pairs, this function
+returns a list of ARRAY references, each containing two items from the given
+list. It is a more efficient version of
+
+ @pairs = pairmap { [ $a, $b ] } @kvlist
+
+It is most convenient to use in a C<foreach> loop, for example:
+
+ foreach my $pair ( pairs @KVLIST ) {
+ my ( $key, $value ) = @$pair;
+ ...
+ }
+
+Since version C<1.39> these ARRAY references are blessed objects, recognising
+the two methods C<key> and C<value>. The following code is equivalent:
+
+ foreach my $pair ( pairs @KVLIST ) {
+ my $key = $pair->key;
+ my $value = $pair->value;
+ ...
+ }
+
+=head2 unpairs
+
+ my @kvlist = unpairs @pairs
+
+I<Since version 1.42.>
+
+The inverse function to C<pairs>; this function takes a list of ARRAY
+references containing two elements each, and returns a flattened list of the
+two values from each of the pairs, in order. This is notionally equivalent to
-=head2 $count = pairgrep { BLOCK } @kvlist
+ my @kvlist = map { @{$_}[0,1] } @pairs
+
+except that it is implemented more efficiently internally. Specifically, for
+any input item it will extract exactly two values for the output list; using
+C<undef> if the input array references are short.
+
+Between C<pairs> and C<unpairs>, a higher-order list function can be used to
+operate on the pairs as single scalars; such as the following near-equivalents
+of the other C<pair*> higher-order functions:
+
+ @kvlist = unpairs grep { FUNC } pairs @kvlist
+ # Like pairgrep, but takes $_ instead of $a and $b
+
+ @kvlist = unpairs map { FUNC } pairs @kvlist
+ # Like pairmap, but takes $_ instead of $a and $b
+
+Note however that these versions will not behave as nicely in scalar context.
+
+Finally, this technique can be used to implement a sort on a keyvalue pair
+list; e.g.:
+
+ @kvlist = unpairs sort { $a->key cmp $b->key } pairs @kvlist
+
+=head2 pairkeys
+
+ my @keys = pairkeys @kvlist;
+
+I<Since version 1.29.>
+
+A convenient shortcut to operating on even-sized lists of pairs, this function
+returns a list of the the first values of each of the pairs in the given list.
+It is a more efficient version of
+
+ @keys = pairmap { $a } @kvlist
+
+=head2 pairvalues
+
+ my @values = pairvalues @kvlist;
+
+I<Since version 1.29.>
+
+A convenient shortcut to operating on even-sized lists of pairs, this function
+returns a list of the the second values of each of the pairs in the given list.
+It is a more efficient version of
+
+ @values = pairmap { $b } @kvlist
+
+=head2 pairgrep
+
+ my @kvlist = pairgrep { BLOCK } @kvlist;
+
+ my $count = pairgrep { BLOCK } @kvlist;
I<Since version 1.29.>
C<$b> to elements of the given list. Any modifications of it by the code block
will be visible to the caller.
-=head2 ( $key, $val ) = pairfirst { BLOCK } @kvlist
+=head2 pairfirst
+
+ my ( $key, $val ) = pairfirst { BLOCK } @kvlist;
-=head2 $found = pairfirst { BLOCK } @kvlist
+ my $found = pairfirst { BLOCK } @kvlist;
I<Since version 1.30.>
-Similar to the C<first> function, but interprets the given list as an
+Similar to the L</first> function, but interprets the given list as an
even-sized list of pairs. It invokes the C<BLOCK> multiple times, in scalar
context, with C<$a> and C<$b> set to successive pairs of values from the
C<@kvlist>.
C<$b> to elements of the given list. Any modifications of it by the code block
will be visible to the caller.
-=head2 @list = pairmap { BLOCK } @kvlist
+=head2 pairmap
-=head2 $count = pairmap { BLOCK } @kvlist
+ my @list = pairmap { BLOCK } @kvlist;
+
+ my $count = pairmap { BLOCK } @kvlist;
I<Since version 1.29.>
See L</KNOWN BUGS> for a known-bug with C<pairmap>, and a workaround.
-=head2 @pairs = pairs @kvlist
-
-I<Since version 1.29.>
-
-A convenient shortcut to operating on even-sized lists of pairs, this function
-returns a list of ARRAY references, each containing two items from the given
-list. It is a more efficient version of
-
- @pairs = pairmap { [ $a, $b ] } @kvlist
-
-It is most convenient to use in a C<foreach> loop, for example:
-
- foreach my $pair ( pairs @KVLIST ) {
- my ( $key, $value ) = @$pair;
- ...
- }
-
-Since version C<1.39> these ARRAY references are blessed objects, recognising
-the two methods C<key> and C<value>. The following code is equivalent:
-
- foreach my $pair ( pairs @KVLIST ) {
- my $key = $pair->key;
- my $value = $pair->value;
- ...
- }
-
-=head2 @keys = pairkeys @kvlist
-
-I<Since version 1.29.>
-
-A convenient shortcut to operating on even-sized lists of pairs, this function
-returns a list of the the first values of each of the pairs in the given list.
-It is a more efficient version of
-
- @keys = pairmap { $a } @kvlist
-
-=head2 @values = pairvalues @kvlist
-
-I<Since version 1.29.>
-
-A convenient shortcut to operating on even-sized lists of pairs, this function
-returns a list of the the second values of each of the pairs in the given list.
-It is a more efficient version of
-
- @values = pairmap { $b } @kvlist
-
=cut
=head1 OTHER FUNCTIONS
=cut
-=head2 @values = shuffle @values
+=head2 shuffle
+
+ my @values = shuffle @values;
Returns the values of the input in a random order
L<https://rt.cpan.org/Ticket/Display.html?id=95409>
-If the block of code given to C<pairmap> contains lexical variables that are
+If the block of code given to L</pairmap> contains lexical variables that are
captured by a returned closure, and the closure is executed after the block
has been re-used for the next iteration, these lexicals will not see the
correct values. For example:
https://perl5.git.perl.org / perl5.git / blobdiff