Params::Classify
Section: User Contributed Perl Documentation (3)
Updated: 2021-01-27
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NAME
Params::Classify - argument type classification
SYNOPSIS
use Params::Classify qw(
scalar_class
is_undef check_undef
is_string check_string
is_number check_number
is_glob check_glob
is_regexp check_regexp
is_ref check_ref ref_type
is_blessed check_blessed blessed_class
is_strictly_blessed check_strictly_blessed
is_able check_able);
$c = scalar_class($arg);
if(is_undef($arg)) {
check_undef($arg);
if(is_string($arg)) {
check_string($arg);
if(is_number($arg)) {
check_number($arg);
if(is_glob($arg)) {
check_glob($arg);
if(is_regexp($arg)) {
check_regexp($arg);
if(is_ref($arg)) {
check_ref($arg);
$t = ref_type($arg);
if(is_ref($arg, "HASH")) {
check_ref($arg, "HASH");
if(is_blessed($arg)) {
check_blessed($arg);
if(is_blessed($arg, "IO::Handle")) {
check_blessed($arg, "IO::Handle");
$c = blessed_class($arg);
if(is_strictly_blessed($arg, "IO::Pipe::End")) {
check_strictly_blessed($arg, "IO::Pipe::End");
if(is_able($arg, ["print", "flush"])) {
check_able($arg, ["print", "flush"]);
DESCRIPTION
This module provides various type-testing functions. These are intended
for functions that, unlike most Perl code, care what type of data they
are operating on. For example, some functions wish to behave differently
depending on the type of their arguments (like overloaded functions
in C
++).
There are two flavours of function in this module. Functions of the first
flavour only provide type classification, to allow code to discriminate
between argument types. Functions of the second flavour package up the
most common type of type discrimination: checking that an argument is
of an expected type. The functions come in matched pairs, of the two
flavours, and so the type enforcement functions handle only the simplest
requirements for arguments of the types handled by the classification
functions. Enforcement of more complex types may, of course, be built
using the classification functions, or it may be more convenient to use
a module designed for the more complex job, such as Params::Validate.
This module is implemented in XS, with a pure Perl backup version for
systems that can't handle XS.
TYPE CLASSIFICATION
This module divides up scalar values into the following classes:
- •
-
undef
- •
-
string (defined ordinary scalar)
- •
-
typeglob (yes, typeglobs fit into scalar variables)
- •
-
regexp (first-class regular expression objects in Perl 5.11 onwards)
- •
-
reference to unblessed object (further classified by physical data type
of the referenced object)
- •
-
reference to blessed object (further classified by class blessed into)
These classes are mutually exclusive and should be exhaustive. This
classification has been chosen as the most useful when one wishes to
discriminate between types of scalar. Other classifications are possible.
(For example, the two reference classes are distinguished by a feature of
the referenced object; Perl does not internally treat this as a feature
of the reference.)
FUNCTIONS
Each of these functions takes one scalar argument (
ARG) to be tested,
possibly with other arguments specifying details of the test. Any scalar
value is acceptable for the argument to be tested. Each
"is_" function
returns a simple truth value result, which is true iff
ARG is of the
type being checked for. Each
"check_" function will return normally
if the argument is of the type being checked for, or will
"die" if it
is not.
Classification
- scalar_class(ARG)
-
Determines which of the five classes described above ARG falls into.
Returns "UNDEF``, ''STRING``, ''GLOB``, ''REGEXP``, ''REF``, or
''BLESSED" accordingly.
The Undefined Value
- is_undef(ARG)
-
- check_undef(ARG)
-
Check whether ARG is "undef". "is_undef(ARG)" is precisely
equivalent to "!defined(ARG)", and is included for completeness.
Strings
- is_string(ARG)
-
- check_string(ARG)
-
Check whether ARG is defined and is an ordinary scalar value (not a
reference, typeglob, or regexp). This is what one usually thinks of as a
string in Perl. In fact, any scalar (including "undef" and references)
can be coerced to a string, but if you're trying to classify a scalar
then you don't want to do that.
- is_number(ARG)
-
- check_number(ARG)
-
Check whether ARG is defined and an ordinary scalar (i.e.,
satisfies ``is_string'' above) and is an acceptable number to Perl.
This is what one usually thinks of as a number.
Note that simple (``is_string''-satisfying) scalars may have independent
numeric and string values, despite the usual pretence that they have
only one value. Such a scalar is deemed to be a number if either it
already has a numeric value (e.g., was generated by a numeric literal
or an arithmetic computation) or its string value has acceptable
syntax for a number (so it can be converted). Where a scalar has
separate numeric and string values (see ``dualvar'' in Scalar::Util), it is
possible for it to have an acceptable numeric value while its string
value does not have acceptable numeric syntax. Be careful to use
such a value only in a numeric context, if you are using it as a number.
``scalar_num_part'' in Scalar::Number extracts the numeric part of a
scalar as an ordinary number. ("0+ARG" suffices for that unless you
need to preserve floating point signed zeroes.)
A number may be either a native integer or a native floating point
value, and there are several subtypes of floating point value.
For classification, and other handling of numbers in scalars, see
Scalar::Number. For details of the two numeric data types, see
Data::Integer and Data::Float.
This function differs from "looks_like_number" (see
``looks_like_number'' in Scalar::Util; also ``looks_like_number'' in perlapi
for a lower-level description) in excluding "undef", typeglobs,
and references. Why "looks_like_number" returns true for "undef"
or typeglobs is anybody's guess. References, if treated as numbers,
evaluate to the address in memory that they reference; this is useful
for comparing references for equality, but it is not otherwise useful
to treat references as numbers. Blessed references may have overloaded
numeric operators, but if so then they don't necessarily behave like
ordinary numbers. "looks_like_number" is also confused by dualvars:
it looks at the string portion of the scalar.
Typeglobs
- is_glob(ARG)
-
- check_glob(ARG)
-
Check whether ARG is a typeglob.
Regexps
- is_regexp(ARG)
-
- check_regexp(ARG)
-
Check whether ARG is a regexp object.
References to Unblessed Objects
- is_ref(ARG)
-
- check_ref(ARG)
-
Check whether ARG is a reference to an unblessed object. If it
is, then the referenced data type can be determined using "ref_type"
(see below), which will return a string such as ``HASH'' or ``SCALAR''.
- ref_type(ARG)
-
Returns "undef" if ARG is not a reference to an unblessed object.
Otherwise, determines what type of object is referenced. Returns
"SCALAR``, ''ARRAY``, ''HASH``, ''CODE``, ''FORMAT``, or ''IO"
accordingly.
Note that, unlike "ref", this does not distinguish between different
types of referenced scalar. A reference to a string and a reference to
a reference will both return "SCALAR". Consequently, what "ref_type"
returns for a particular reference will not change due to changes in
the value of the referent, except for the referent being blessed.
- is_ref(ARG, TYPE)
-
- check_ref(ARG, TYPE)
-
Check whether ARG is a reference to an unblessed object of type
TYPE, as determined by ``ref_type''. TYPE must be a string.
Possible TYPEs are "SCALAR``, ''ARRAY``, ''HASH``, ''CODE``,
''FORMAT``, and ''IO".
References to Blessed Objects
- is_blessed(ARG)
-
- check_blessed(ARG)
-
Check whether ARG is a reference to a blessed object. If it is,
then the class into which the object was blessed can be determined using
``blessed_class''.
- is_blessed(ARG, CLASS)
-
- check_blessed(ARG, CLASS)
-
Check whether ARG is a reference to a blessed object that claims to
be an instance of CLASS (via its "isa" method; see ``isa'' in perlobj).
CLASS must be a string, naming a Perl class.
- blessed_class(ARG)
-
Returns "undef" if ARG is not a reference to a blessed object.
Otherwise, returns the class into which the object is blessed.
"ref" (see ``ref'' in perlfunc) gives the same result on references
to blessed objects, but different results on other types of value.
"blessed_class" is actually identical to ``blessed'' in Scalar::Util.
- is_strictly_blessed(ARG)
-
- check_strictly_blessed(ARG)
-
Check whether ARG is a reference to a blessed object, identically
to ``is_blessed''. This exists only for symmetry; the useful form of
"is_strictly_blessed" appears below.
- is_strictly_blessed(ARG, CLASS)
-
- check_strictly_blessed(ARG, CLASS)
-
Check whether ARG is a reference to an object blessed into CLASS
exactly. CLASS must be a string, naming a Perl class. Because this
excludes subclasses, this is rarely what one wants, but there are some
specialised occasions where it is useful.
- is_able(ARG)
-
- check_able(ARG)
-
Check whether ARG is a reference to a blessed object, identically
to ``is_blessed''. This exists only for symmetry; the useful form of
"is_able" appears below.
- is_able(ARG, METHODS)
-
- check_able(ARG, METHODS)
-
Check whether ARG is a reference to a blessed object that claims to
implement the methods specified by METHODS (via its "can" method;
see ``can'' in perlobj). METHODS must be either a single method name or
a reference to an array of method names. Each method name is a string.
This interface check is often more appropriate than a direct ancestry
check (such as ``is_blessed'' performs).
BUGS
Probably ought to handle something like Params::Validate's scalar
type specification system, which makes much the same distinctions.
SEE ALSO
Data::Float,
Data::Integer,
Params::Validate,
Scalar::Number,
Scalar::Util
AUTHOR
Andrew Main (Zefram) <
zefram@fysh.org>
COPYRIGHT
Copyright (C) 2004, 2006, 2007, 2009, 2010, 2017
Andrew Main (Zefram) <
zefram@fysh.org>
Copyright (C) 2009, 2010 PhotoBox Ltd
LICENSE
This module is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.