Ref::Util(3) User Contributed Perl Documentation Ref::Util(3)
NAME
Ref::Util - Utility functions for checking references
VERSION
version 0.204
SYNOPSIS
use Ref::Util qw( is_plain_arrayref is_plain_hashref );
if ( is_plain_arrayref( $something ) ) {
print for @{ $something };
} elsif ( is_plain_hashref( $something ) ) {
print for sort values %{ $something };
}
DESCRIPTION
Ref::Util introduces several functions to help identify references in a
smarter (and usually faster) way. In short:
# conventional approach # with Ref::Util
ref( $foo ) eq 'ARRAY' is_plain_arrayref( $foo )
use Scalar::Util qw( reftype );
reftype( $foo ) eq 'ARRAY' is_arrayref( $foo )
The difference:
o No comparison against a string constant
When you call "ref", you stringify the reference and then compare
it to some string constant (like "ARRAY" or "HASH"). Not just
awkward, it's brittle since you can mispell the string.
If you use Scalar::Util's "reftype", you still compare it as a
string:
if ( reftype($foo) eq 'ARRAY' ) { ... }
o Supports blessed variables
Note: In future versions, the idea is to make the default functions
use the plain variation, which means explicitly non-blessed
references.
If you want to explicitly check for blessed references, you should
use the "is_blessed_*" functions. There will be an "is_any_*"
variation which will act like the current main functions - not
caring whether it's blessed or not.
When calling "ref", you receive either the reference type (SCALAR,
ARRAY, HASH, etc.) or the package it's blessed into.
When calling "is_arrayref" (et. al.), you check the variable flags,
so even if it's blessed, you know what type of variable is blessed.
my $foo = bless {}, 'PKG';
ref($foo) eq 'HASH'; # fails
use Ref::Util 'is_hashref';
my $foo = bless {}, 'PKG';
is_hashref($foo); # works
On the other hand, in some situations it might be better to
specifically exclude blessed references. The rationale for that
might be that merely because some object happens to be implemented
using a hash doesn't mean it's necessarily correct to treat it as a
hash. For these situations, you can use "is_plain_hashref" and
friends, which have the same performance benefits as "is_hashref".
There is also a family of functions with names like
"is_blessed_hashref"; these return true for blessed object
instances that are implemented using the relevant underlying type.
o Supports tied variables and magic
Tied variables (used in Readonly, for example) are supported.
use Ref::Util qw<is_plain_hashref>;
use Readonly;
Readonly::Scalar my $rh2 => { a => { b => 2 } };
is_plain_hashref($rh2); # success
Ref::Util added support for this in 0.100. Prior to this version
the test would fail.
o Ignores overloading
These functions ignore overloaded operators and simply check the
variable type. Overloading will likely not ever be supported, since
I deem it problematic and confusing.
Overloading makes your variables opaque containers and hides away
what they are and instead require you to figure out how to use
them. This leads to code that has to test different abilities (in
"eval", so it doesn't crash) and to interfaces that get around what
a person thought you would do with a variable. This would have been
alright, except there is no clear way of introspecting it.
o Ignores subtle types:
The following types, provided by Scalar::Util's "reftype", are not
supported:
o "VSTRING"
This is a "PVMG" ("normal" variable) with a flag set for
VSTRINGs. Since this is not a reference, it is not supported.
o "LVALUE"
A variable that delegates to another scalar. Since this is not
a reference, it is not supported.
o "INVLIST"
I couldn't find documentation for this type.
Support might be added, if a good reason arises.
o Usually fast
When possible, Ref::Util uses Ref::Util::XS as its implementation.
(If you don't have a C compiler available, it uses a pure Perl
fallback that has all the other advantages of Ref::Util, but isn't
as fast.)
In fact, Ref::Util::XS has two alternative implementations
available internally, depending on the features supported by the
version of Perl you're using. For Perls that supports custom OPs,
we actually add an OP (which is faster); for other Perls, the
implementation that simply calls an XS function (which is still
faster than the pure-Perl equivalent).
See below for benchmark results.
EXPORT
Nothing is exported by default. You can ask for specific subroutines
(described below) or ask for all subroutines at once:
use Ref::Util qw<is_scalarref is_arrayref is_hashref ...>;
# or
use Ref::Util ':all';
SUBROUTINES
is_ref($ref)
Check for a reference to anything.
is_ref([]);
is_scalarref($ref)
Check for a scalar reference.
is_scalarref(\"hello");
is_scalarref(\30);
is_scalarref(\$value);
Note that, even though a reference is itself a type of scalar value, a
reference to another reference is not treated as a scalar reference:
!is_scalarref(\\1);
The rationale for this is two-fold. First, callers that want to decide
how to handle inputs based on their reference type will usually want to
treat a ref-ref and a scalar-ref differently. Secondly, this more
closely matches the behavior of the "ref" built-in and of "reftype" in
Scalar::Util, which report a ref-ref as "REF" rather than "SCALAR".
is_arrayref($ref)
Check for an array reference.
is_arrayref([]);
is_hashref($ref)
Check for a hash reference.
is_hashref({});
is_coderef($ref)
Check for a code reference.
is_coderef( sub {} );
is_regexpref($ref)
Check for a regular expression (regex, regexp) reference.
is_regexpref( qr// );
is_globref($ref)
Check for a glob reference.
is_globref( \*STDIN );
is_formatref($ref)
Check for a format reference.
# set up format in STDOUT
format STDOUT =
.
# now we can test it
is_formatref( *main::STDOUT{'FORMAT'} );
This function is not available in Perl 5.6 and will trigger a
"croak()".
is_ioref($ref)
Check for an IO reference.
is_ioref( *STDOUT{IO} );
is_refref($ref)
Check for a reference to a reference.
is_refref( \[] ); # reference to array reference
is_plain_scalarref($ref)
Check for an unblessed scalar reference.
is_plain_scalarref(\"hello");
is_plain_scalarref(\30);
is_plain_scalarref(\$value);
is_plain_ref($ref)
Check for an unblessed reference to anything.
is_plain_ref([]);
is_plain_arrayref($ref)
Check for an unblessed array reference.
is_plain_arrayref([]);
is_plain_hashref($ref)
Check for an unblessed hash reference.
is_plain_hashref({});
is_plain_coderef($ref)
Check for an unblessed code reference.
is_plain_coderef( sub {} );
is_plain_globref($ref)
Check for an unblessed glob reference.
is_plain_globref( \*STDIN );
is_plain_formatref($ref)
Check for an unblessed format reference.
# set up format in STDOUT
format STDOUT =
.
# now we can test it
is_plain_formatref(bless *main::STDOUT{'FORMAT'} );
is_plain_refref($ref)
Check for an unblessed reference to a reference.
is_plain_refref( \[] ); # reference to array reference
is_blessed_scalarref($ref)
Check for a blessed scalar reference.
is_blessed_scalarref(bless \$value);
is_blessed_ref($ref)
Check for a blessed reference to anything.
is_blessed_ref(bless [], $class);
is_blessed_arrayref($ref)
Check for a blessed array reference.
is_blessed_arrayref(bless [], $class);
is_blessed_hashref($ref)
Check for a blessed hash reference.
is_blessed_hashref(bless {}, $class);
is_blessed_coderef($ref)
Check for a blessed code reference.
is_blessed_coderef( bless sub {}, $class );
is_blessed_globref($ref)
Check for a blessed glob reference.
is_blessed_globref( bless \*STDIN, $class );
is_blessed_formatref($ref)
Check for a blessed format reference.
# set up format for FH
format FH =
.
# now we can test it
is_blessed_formatref(bless *FH{'FORMAT'}, $class );
is_blessed_refref($ref)
Check for a blessed reference to a reference.
is_blessed_refref( bless \[], $class ); # reference to array reference
BENCHMARKS
Here is a benchmark comparing similar checks.
my $bench = Dumbbench->new(
target_rel_precision => 0.005,
initial_runs => 20,
);
my $amount = 1e7;
my $ref = [];
$bench->add_instances(
Dumbbench::Instance::PerlSub->new(
name => 'Ref::Util::is_plain_arrayref (CustomOP)',
code => sub {
Ref::Util::is_plain_arrayref($ref) for ( 1 .. $amount )
},
),
Dumbbench::Instance::PerlSub->new(
name => 'ref(), reftype(), !blessed()',
code => sub {
ref $ref
&& Scalar::Util::reftype($ref) eq 'ARRAY'
&& !Scalar::Util::blessed($ref)
for ( 1 .. $amount );
},
),
Dumbbench::Instance::PerlSub->new(
name => 'ref()',
code => sub { ref($ref) eq 'ARRAY' for ( 1 .. $amount ) },
),
Dumbbench::Instance::PerlSub->new(
name => 'Data::Util::is_array_ref',
code => sub { is_array_ref($ref) for ( 1 .. $amount ) },
),
);
The results:
ref(): 5.335e+00 +/- 1.8e-02 (0.3%)
ref(), reftype(), !blessed(): 1.5545e+01 +/- 3.1e-02 (0.2%)
Ref::Util::is_plain_arrayref (CustomOP): 2.7951e+00 +/- 6.2e-03 (0.2%)
Data::Util::is_array_ref: 5.9074e+00 +/- 7.5e-03 (0.1%)
(Rounded run time per iteration)
A benchmark against Data::Util:
Ref::Util::is_plain_arrayref: 3.47157e-01 +/- 6.8e-05 (0.0%)
Data::Util::is_array_ref: 6.7562e-01 +/- 7.5e-04 (0.1%)
SEE ALSO
o Params::Classify(3)
o Scalar::Util(3)
o Data::Util(3)
THANKS
The following people have been invaluable in their feedback and
support.
o Yves Orton
o Steffen MA1/4ller
o Jarkko Hietaniemi
o Mattia Barbon
o Zefram
o Tony Cook
o Sergey Aleynikov
AUTHORS
o Aaron Crane
o Vikentiy Fesunov
o Sawyer X
o Gonzalo Diethelm
o p5pclub
LICENSE
This software is made available under the MIT Licence as stated in the
accompanying LICENSE file.
AUTHORS
o Sawyer X <xsawyerx@cpan.org>
o Aaron Crane <arc@cpan.org>
o Vikenty Fesunov <vyf@cpan.org>
o Gonzalo Diethelm <gonzus@cpan.org>
o Karen Etheridge <ether@cpan.org>
COPYRIGHT AND LICENSE
This software is Copyright (c) 2017 by Sawyer X.
This is free software, licensed under:
The MIT (X11) License
perl v5.30.0 2018-04-19 Ref::Util(3)
ref-util 0.204.0 - Generated Fri Jul 24 10:45:22 CDT 2020