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Data::Util - A selection of utilities for data and data types


This document describes Data::Util version 0.67


        use Data::Util qw(:validate);

        sub foo{
                # they will die if invalid values are supplied
                my $sref = scalar_ref(shift);
                my $aref = array_ref(shift);
                my $href = hash_ref(shift);
                my $cref = code_ref(shift);
                my $gref = glob_ref(shift);
                my $rx   = rx(shift); # regular expression
                my $obj  = instance(shift, 'Foo');
                # ...

        use Data::Util qw(:check);

        sub bar{
                my $x = shift;
                if(is_scalar_ref $x){
                        # $x is an array reference
                # ...
                elsif(is_instance $x, 'Foo'){
                        # $x is an instance of Foo
                # ...

        # miscelaneous
        use Data::Util qw(:all);

        my $x = anon_scalar();
        $x = anon_scalar($x); # OK

        my $stash = get_stash('Foo');

                hello  => sub{ "Hello!\n" },
                goodby => sub{ "Goodby!\n" },

        print Foo::hello(); # Hello!

        my($pkg, $name) = get_code_info(\&Foo::hello); # => ('Foo', 'hello')
        my $fqn         = get_code_info(\&Foo::hello); # =>  'Foo::hello'
        my $code        = get_code_ref('Foo', 'hello');  # => \&Foo::hello

        uninstall_subroutine('Foo', qw(hello goodby));

    # simple format for errro messages (not the same as Data::Dumper)
        print neat("Hello!\n"); # => "Hello!\n"
        print neat(3.14);       # => 3.14
        print neat(undef);      # => undef


This module provides utility functions for data and data types, including functions for subroutines and symbol table hashes (stashes).

This module makes for a pure Perl and XS implementation.

However, if you want to use the full capacity of it, we recommend you to opt for the XS backend.

There are many benchmarks in the DIST-DIR/benchmark/ directory.


Check functions

Check functions are introduced by the :check import tag, which check the argument type and return a bool.

These functions also check for overloading magic, e.g. ${} corresponds to a SCALAR reference.


Checks for a SCALAR reference.


Checks for an ARRAY reference.


Checks for a HASH reference.


Checks for a CODE reference.


Checks for a GLOB reference.


Checks for a regular expression reference generated by the qr// operator.

is_instance(value, class)

Checks for an instance of class.

It is equivalent to the following statement: Scalar::Util::blessed($value) && $value->isa($class).


Checks for an invocant, i.e. a blessed reference or existent package name.

If value is a valid class name but does not exist, it will return false.


Checks whether value is a primitive value, i.e. a defined, non-ref, and non-type-glob value.

This function has no counterpart for validation.


Checks whether value is a string with non-zero-length contents, equivalent to is_value($value) && length($value) > 0.

This function has no counterpart for validation.


Checks whether value is a number. Here, a number means that the perl parser can understand it and that the perl numeric converter (e.g. invoked by sprintf '%g', $value) doesn't complain about it.

It is similar to Scalar::Util::looks_like_number() but refuses infinity, not a number and "0 but true". Note that 9**9**9 makes infinity and 9**9**9 - 9**9**9 makes not a number.

This function has no counterpart for validation.


Checks whether value is an integer. An integer is also a number, so this function refuses infinity and not a number. See also is_number().

This function has no counterpart for validation.

Validating functions

Validating functions are introduced by the :validate tag which checks for the argument and returns the first argument. These are like the :check functions but dies if the argument type is invalid.

These functions also checks overloading magic, e.g. ${} for a SCALAR reference.


Validates a SCALAR reference.


Validates an ARRAY reference.


Validates a HASH reference.


Validates a CODE reference.


Validates a GLOB reference.


Validates a regular expression reference.

instance(value, class)

Validates an instance of class.


Validates an invocant, i.e. a blessed reference or existent package name.

If value is a valid class name and the class exists, then it returns the canonical class name, which is logically cleaned up. That is, it runs $value =~ s/^::(?:main::)*//; before returning it.

NOTE: Canonization is done so due to an inconsistency between Perl versions. For instance:

        package ::Foo; # OK
        my $x = bless {}, '::Foo'; # OK
        ref($x)->isa('Foo'); # Fatal

The last code snippet causes a fatal error: Can't call method "isa" without package or object reference. However, invocant(ref $x)->isa('Foo') is always OK.

Miscellaneous utilities

There are some other utility functions you can import from this module.


Generates an anonymous scalar reference to undef.


Generates an anonymous scalar reference to the copy of value.

It is equivalent to do{ my $tmp = $value; \$tmp; }.


Returns a neat string that is suitable to display.

This is a smart version of <do{ defined($value) ? qq{"$value"} : 'undef' }>.


Returns the symbol table hash (also known as stash) of invocant if the stash exists.

install_subroutine(package, name => subr [, ...])

Installs subr into package as name.

It is similar to do{ no strict 'refs'; *{$package.'::'.$name} = \&subr; }. In addition, if subr is an anonymous subroutine, it is located into package as a named subroutine &package::name.

For example:

        install_subroutine($pkg,   say => sub{ print @_, "\n" });
                one => \&_one,
                two => \&_two,

        # accepts a HASH reference
        install_subroutine($pkg, { say => sub{ print @_, "\n" }); #

To re-install subr, use no warnings 'redefine' directive:

        no warnings 'redefine';
        install_subroutine($package, $name => $subr);
uninstall_subroutine(package, names...)

Uninstalls names from package.

It is similar to Sub::Delete::delete_sub(), but uninstall multiple subroutines at a time.

If you want to specify deleted subroutines, you can supply name => \&subr pairs.

For example:

        uninstall_subroutine('Foo', 'hello');

        uninstall_subroutine('Foo', hello => \&Bar::hello);

                one => \&_one,
                two => \&_two,

        # accepts a HASH reference
        uninstall_subroutine(\$pkg, { hello => \&Bar::hello });

Returns a pair of elements, the package name and the subroutine name of subr.

It is similar to Sub::Identify::get_code_info(), but it returns the fully qualified name in scalar context.

get_code_ref(package, name, flag?)

Returns &package::name if it exists, not touching the symbol in the stash.

if flag is a string -create, it returns &package::name regardless of its existence. That is, it is equivalent to do{ no strict 'refs'; \&{package . '::' . $name} }.

For example:

        $code = get_code_ref($pkg, $name);          # like  *{$pkg.'::'.$name}{CODE}
        $code = get_code_ref($pkg, $name, -create); # like \&{$pkg.'::'.$name}
curry(subr, args and/or placeholders)

Makes subr curried and returns the curried subroutine.

This is also considered as lightweight closures.

See also Data::Util::Curry.

modify_subroutine(subr, ...)

Modifies subr with subroutine modifiers and returns the modified subroutine. This is also considered as lightweight closures.

subr must be a code reference or callable object.

Optional arguments: before => [subroutine(s)] called before subr. around => [subroutine(s)] called around subr. after => [subroutine(s)] called after subr.

This seems a constructor of modified subroutines and subroutine_modifier() is property accessors, but it does not bless the modified subroutines.


Returns whether subr is a modified subroutine.

subroutine_modifier(modified_subr, property)

Gets property from modified.

Valid properties are: before, around, after.

subroutine_modifier(modified_subr, modifier => [subroutine(s)])

Adds subroutine modifier to modified_subr.

Valid modifiers are: before, around, after.

mkopt(input, moniker, require_unique, must_be)

Produces an array of an array reference from input.

It is compatible with Data::OptList::mkopt(). In addition to it, must_be can be a HASH reference with name => type pairs.

For example:

        my $optlist = mkopt(['foo', bar => [42]], $moniker, $uniq, { bar => 'ARRAY' });
        # $optlist == [[foo => undef], [bar => [42]]
mkopt_hash(input, moniker, must_be)

Produces a hash reference from input.

It is compatible with Data::OptList::mkopt_hash(). In addition to it, must_be can be a HASH reference with name => type pairs.

For example:

        my $optlist = mkopt(['foo', bar => [42]], $moniker, { bar => 'ARRAY' });
        # $optlist == {foo => undef, bar => [42]}



If true, Data::Util uses the pure Perl implementation.


Perl 5.10 or later.

If you have a C compiler, you can use the XS backend.

A pure Perl backend/implementation is also made available in case you have no C compiler handy (unlikely!).


No bugs have been reported.

Please report any bugs or feature requests to the author.














Goro Fuji(gfx) <gfuji(at)>.


Copyright (c) 2008-2010, Goro Fuji <gfuji(at)>. All rights reserved.

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.