Params::Classify(3)					User Contributed Perl Documentation				       Params::Classify(3)

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:

       o   undef

       o   string (defined ordinary scalar)

       o   typeglob (yes, typeglobs fit into scalar variables)

       o   regexp (first-class regular expression objects in Perl 5.11 onwards)

       o   reference to unblessed object (further classified by physical data type of the referenced object)

       o   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 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.

perl v5.18.2							    2017-10-06						       Params::Classify(3)