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Think about Loose Coupling


by root (Scribe)
on Dec 23, 1999 at 00:49 UTC ( #1131=perlfunc: print w/replies, xml ) Need Help??


See the current Perl documentation for lib:UNIVERSAL.

Here is our local, out-dated (pre-5.6) version:

UNIVERSAL - base class for ALL classes (blessed references)

    $io = $fd->isa("IO::Handle");
    $sub = $obj->can('print');

    $yes = UNIVERSAL::isa($ref, "HASH");

UNIVERSAL is the base class which all bless references will inherit from, see perlobj

UNIVERSAL provides the following methods

isa ( TYPE )

isa returns true if REF is blessed into package TYPE or inherits from package TYPE.

isa can be called as either a static or object method call.

can ( METHOD )

can checks if the object has a method called METHOD. If it does then a reference to the sub is returned. If it does not then undef is returned.

can can be called as either a static or object method call.


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.

VERSION can be called as either a static or object method call.

The isa and can methods can also be called as subroutines


isa returns true if the first argument is a reference and either of the following statements is true.

VAL is a blessed reference and is blessed into package TYPE or inherits from package TYPE

VAL is a reference to a TYPE of perl variable (er 'HASH')


If VAL is a blessed reference which has a method called METHOD, can returns a reference to the subroutine. If VAL is not a blessed reference, or if it does not have a method METHOD, undef is returned.

These subroutines should not be imported via use UNIVERSAL qw(...). If you want simple local access to them you can do

  *isa = \&UNIVERSAL::isa;

to import isa into your package.

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[Corion]: Discipulus: Yeah, I rediscovered it when I wanted to have a simple (cross-platform) wrapper for my OpenGL program so it has a nice window etc
[Corion]: ... and one thing leads to another, so ambrus provided the integration with AnyEvent so I can now conveniently make HTTP requests from that app too :)
[Corion]: I'm afraid that I'll turn off dk some day with all my bug reports or stuff that could be documented better ;-)

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