eff_i_g has asked for the wisdom of the Perl Monks concerning the following question:

Syntactical Saints,

The following statement caught my eye during a recent skimming of the Perl Pocket Reference, Fourth Edition on Page 9 under "Literal Values" => "Scalar Values" => "String": 
    Class::
        A value that is mostly equivalent to "Class".
I don't understand what this is trying to convey.

I know :: is used as a directory separator for Modules, and to specify Package names. Am I missing something else?

Thanks.

P.S. Is :: referred to as "the double colon" within the Perl coummunity, or does it have a neater name?

Update: Here is the surrounding material to provide more context (i.e., as much clarification as I can): 
Literal Values
Scalar Values
    ...
    ...
    String
        'abc'
            Literal string, no variable interpolation...except...
        "abc"
            A string in which variables are interpolated...
        `command`
            Evaluates to the output of the command.
        Class::
            A value that is mostly equivalent to "Class".
        1.2.3    v.5.6.0.1
            A string ("v-string") composed of the specified ordinals. 
+...
        <<identifier
            Shell-style "here document."
        __FILE__
            The name of the program file.
        __PACKAGE__
            The name of the current package.

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Replies are listed 'Best First'.
Re: ::'s role in strings
by mantadin (Beadle) on Apr 27, 2006 at 17:34 UTC
    I do not know, what this book is trying to say, either. Yet I think, :: does have more meanings in addition to those you mentioned, at least in OO-context. AFAIK, 
    Animal->foo()

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    is the same like 
    Animal::foo("Animal")

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    Now, if Dog is an Animal, and has no own implementation of the foo()-method, 
    Dog->foo()

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    is the same as Dog::foo("Animal") update Animal::foo("Dog") (thanks to ikegami)

    Maybe you can clarify your question a little bit further.

    As to your p.s., I know :: as the 'scope resolution operator', but I don't know whether this name is really very common in the Perl community.

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      You got it backwards
      Dog::foo("Animal")
      should be
      Animal::foo("Dog")

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      Your first two examples are not necessarily equivalent. Function invocation uses a very different lookup mechanism from method dispatch.

      The postfix double colons exist to disambiguate classnames from barewords in the parser.

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Re: ::'s role in strings
by ikegami (Patriarch) on Apr 27, 2006 at 18:47 UTC

    It means you can do the following: 

    >perl -e "$a = Class::; print $a"
Class

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    It even works under strict, and it's doesn't issue any warnings if the package exists.

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      Here is what I tried on my machine: 
      > perl -v

This is perl, v5.8.6 built for PA-RISC2.0

Copyright 1987-2004, Larry Wall

...

> perl -e "$a = Class::; print $a"
a: Undefined variable.

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      I guess my follow up question is: Why does/should this work?
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        I used 5.6.1.

        a: Undefined variable.

        I'm susprised by the output you get. Is that really what you got for output? from perl? No, it's from your shell. Use single quotes.

        Why does/should this work?

        It's probably just an unintentional side-effect. It's to avoid ambiguitities when using indirect method calls. I wouldn't use :: as a quoting mechanism.

        Updated: Thanks to japhy and jhourcle for the corrections/elaborations.

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