check::isa(3pm) [debian man page]
Check::ISA(3pm) User Contributed Perl Documentation Check::ISA(3pm) NAME
Check::ISA - DWIM, correct checking of an object's class SYNOPSIS
use Check::ISA; if ( obj($foo, "SomeClass") ) { $foo->some_method; } # instead of one of these methods: UNIVERSAL::isa($foo, "SomeClass") # WRONG ref $obj eq "SomeClass"; # VERY WRONG $foo->isa("SomeClass") # May die local $@; eval { $foo->isa("SomeClass") } # too long DESCRIPTION
This module provides several functions to assist in testing whether a value is an object, and if so asking about its class. FUNCTIONS
obj $thing, [ $class ] This function tests if $thing is an object. If $class is provided, it also tests tests whether "$thing->isa($class)". $thing is considered an object if it's blessed, or if it's a "GLOB" with a valid "IO" slot (the "IO" slot contains a FileHandle object which is the actual invocant). This corresponds directly to "gv_fetchmethod". obj_does $thing, [ $class_or_role ] Just like "obj" but uses "DOES" in UNIVERSAL instead of "isa" in UNIVERSAL. "DOES" in UNIVERSAL is just like "isa", except it's use is encouraged to query about an interface, as opposed to the object structure. If "DOES" is not overridden by th ebject, calling it is semantically identical to calling "isa". This is probably reccomended over "obj" for interoperability, but can be slower on Perls before 5.10. Note that "DOES" in UNIVERSAL inv $thing, [ $class_or_role ] Just like "obj_does", but also returns true for classes. Note that this method is slower, but is supposed to return true for any value you can call methods on (class, object, filehandle, etc). Look into autobox if you would like to be able to call methods on all values. obj_can $thing, $method inv_can $thing, $method Checks if $thing is an object or class, and calls "can" on $thing if appropriate. SEE ALSO
UNIVERSAL, Params::Util, autobox, Moose, asa VERSION CONTROL
This module is maintained using Darcs. You can get the latest version from <http://nothingmuch.woobling.org/code>, and use "darcs send" to commit changes. AUTHOR
Yuval Kogman <nothingmuch@woobling.org> COPYRIGHT
Copyright (c) 2008 Yuval Kogman. All rights reserved This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. perl v5.10.0 2008-07-25 Check::ISA(3pm)
Check Out this Related Man Page
UNIVERSAL(3perl) Perl Programmers Reference Guide UNIVERSAL(3perl) NAME
UNIVERSAL - base class for ALL classes (blessed references) SYNOPSIS
$is_io = $fd->isa("IO::Handle"); $is_io = Class->isa("IO::Handle"); $does_log = $obj->DOES("Logger"); $does_log = Class->DOES("Logger"); $sub = $obj->can("print"); $sub = Class->can("print"); $sub = eval { $ref->can("fandango") }; $ver = $obj->VERSION; # but never do this! $is_io = UNIVERSAL::isa($fd, "IO::Handle"); $sub = UNIVERSAL::can($obj, "print"); DESCRIPTION
"UNIVERSAL" is the base class from which all blessed references inherit. See perlobj. "UNIVERSAL" provides the following methods: "$obj->isa( TYPE )" "CLASS->isa( TYPE )" "eval { VAL->isa( TYPE ) }" Where "TYPE" is a package name $obj is a blessed reference or a package name "CLASS" is a package name "VAL" is any of the above or an unblessed reference When used as an instance or class method ("$obj->isa( TYPE )"), "isa" returns true if $obj is blessed into package "TYPE" or inherits from package "TYPE". When used as a class method ("CLASS->isa( TYPE )", sometimes referred to as a static method), "isa" returns true if "CLASS" inherits from (or is itself) the name of the package "TYPE" or inherits from package "TYPE". If you're not sure what you have (the "VAL" case), wrap the method call in an "eval" block to catch the exception if "VAL" is undefined. If you want to be sure that you're calling "isa" as a method, not a class, check the invocand with "blessed" from Scalar::Util first: use Scalar::Util 'blessed'; if ( blessed( $obj ) && $obj->isa("Some::Class") { ... } "$obj->DOES( ROLE )" "CLASS->DOES( ROLE )" "DOES" checks if the object or class performs the role "ROLE". A role is a named group of specific behavior (often methods of particular names and signatures), similar to a class, but not necessarily a complete class by itself. For example, logging or serialization may be roles. "DOES" and "isa" are similar, in that if either is true, you know that the object or class on which you call the method can perform specific behavior. However, "DOES" is different from "isa" in that it does not care how the invocand performs the operations, merely that it does. ("isa" of course mandates an inheritance relationship. Other relationships include aggregation, delegation, and mocking.) By default, classes in Perl only perform the "UNIVERSAL" role, as well as the role of all classes in their inheritance. In other words, by default "DOES" responds identically to "isa". There is a relationship between roles and classes, as each class implies the existence of a role of the same name. There is also a relationship between inheritance and roles, in that a subclass that inherits from an ancestor class implicitly performs any roles its parent performs. Thus you can use "DOES" in place of "isa" safely, as it will return true in all places where "isa" will return true (provided that any overridden "DOES" and "isa" methods behave appropriately). "$obj->can( METHOD )" "CLASS->can( METHOD )" "eval { VAL->can( METHOD ) }" "can" checks if the object or class has a method called "METHOD". If it does, then it returns a reference to the sub. If it does not, then it returns undef. This includes methods inherited or imported by $obj, "CLASS", or "VAL". "can" cannot know whether an object will be able to provide a method through AUTOLOAD (unless the object's class has overridden "can" appropriately), so a return value of undef does not necessarily mean the object will not be able to handle the method call. To get around this some module authors use a forward declaration (see perlsub) for methods they will handle via AUTOLOAD. For such 'dummy' subs, "can" will still return a code reference, which, when called, will fall through to the AUTOLOAD. If no suitable AUTOLOAD is provided, calling the coderef will cause an error. You may call "can" as a class (static) method or an object method. Again, the same rule about having a valid invocand applies -- use an "eval" block or "blessed" if you need to be extra paranoid. "VERSION ( [ REQUIRE ] )" "VERSION" will return the value of the variable $VERSION in the package the object is blessed into. If "REQUIRE" is given then it will do a comparison and die if the package version is not greater than or equal to "REQUIRE". Both $VERSION or "REQUIRE" must be "lax" version numbers (as defined by the version module) or "VERSION" will die with an error. "VERSION" can be called as either a class (static) method or an object method. WARNINGS
NOTE: "can" directly uses Perl's internal code for method lookup, and "isa" uses a very similar method and cache-ing strategy. This may cause strange effects if the Perl code dynamically changes @ISA in any package. You may add other methods to the UNIVERSAL class via Perl or XS code. You do not need to "use UNIVERSAL" to make these methods available to your program (and you should not do so). EXPORTS
None by default. You may request the import of three functions ("isa", "can", and "VERSION"), but this feature is deprecated and will be removed. Please don't do this in new code. For example, previous versions of this documentation suggested using "isa" as a function to determine the type of a reference: use UNIVERSAL 'isa'; $yes = isa $h, "HASH"; $yes = isa "Foo", "Bar"; The problem is that this code will never call an overridden "isa" method in any class. Instead, use "reftype" from Scalar::Util for the first case: use Scalar::Util 'reftype'; $yes = reftype( $h ) eq "HASH"; and the method form of "isa" for the second: $yes = Foo->isa("Bar"); perl v5.14.2 2011-09-26 UNIVERSAL(3perl)