{use strict "package"}++. Symbolic references to packages are problematic. Just avoid them?

- tye        

Just to be sure we mean the same thing. This syntax describes what I am trying to achieve:

package this_package can not be reentered;
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Your is also or is instead seems to indicate creating aliases for a namespace. I like that idea a lot--in a few languages I wished I could simply capture intention during prototyping by:

class ID_NUMBER is INT;
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and settle details later.

Be well,
rir

While you're at it, your lint process may want to catch that there should only be one package statement per file, and that package statement should match the filename, including path, from some entry in @INC, with directory separators becoming ::, and a .pm thrown on at the end. All of this is further convention that is usually a Good Practice (tm).

Or, you could embrace the freedom that perl gives to do what you think is right instead of what Larry thinks is right. Which means not following convention when convention is getting in the way of getting your job done. I've had cause to buck convention in the past, and your lint would probably give me problems over it. The key is to allow people to do what needs to be done, as long as they acknowledge they're doing something strange. Just like we always "use strict", but have the ability to lexically scope "no strict" (preferably with a modifier, such as 'refs').

Tanktalus, your tone seems to disparage my intentions. If you read my post as a request to change Perl then I was not clear, I would just like that effect. Given the nature of the problem the easiest technically correct code-fix probably is to hack the perl source and add a check and fail to where package statements are handled. That would likely be a fairly localized patch.

Collision of module names is a issue. In my code, client code is invited to partition a problem by creating sub-classes. It is very possible that the same namespace could be inadvertently reused. I am not trying to enforce the common conventions of a Good Practice(TM).

Be well, rir

While you're at it, your lint process may want to catch that there should only be one package statement per file, and that package statement should match the filename, including path, from some entry in @INC, with directory separators becoming ::, and a .pm thrown on at the end.

My (limited) reading of modules leads me to think this is overkill. I've seen multiple package statements in a module for classes/namespaces derived from the main module, but the package was too small to worry about creating separate files. (I wonder how many modules in the core distribution make use of multiple package statements?)

-QM
--
Quantum Mechanics: The dreams stuff is made of

That's actually kind of my point. Convention says this is what you're supposed to do. However, convention also allows for alternatives. Convention says that each package appears once, at the top of a .pm file of the same name where ::'s are converted to directory separators. Which means that you should only have one package per file, and that you should never overlap with others' packages.

In reality, there can be valid reasons for bucking convention. Packages that are too small to worry about separate files is a valid one. Hiding a package is another one - e.g., how mirod hides XML::Twig::Elt inside the XML/Twig.pm. Although in this case, it may be partly because XML::Twig and XML::Twig::Elt are so tightly intertwined that there could be fun times in trying to compile them in separate units. Other cases may have tightly tied packages where using the wrong one first can't resolve BEGIN blocks appropriately. Or other tightly tied packages where the other packages would take longer to locate on disk than is worth it.

I really don't have a problem with the OP's suggestion. As long as there is a clean and easy way to turn it off when I know what I'm doing. Such as what TimToady suggests.

use CGI::Application;
class CGI::Application is also {
  # stuff we want to add to the CGI::Application namespace.
};
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This says, "Yes, I know there is already a CGI::Application, but I'm the human, and you're the dumb computer, so do what I tell you." Well, that's what it says if I do it. It might not be so snarky if others do it ;-) I don't have an issue with this - the extra typing required for the rare time I do it seems like a reasonable trade-off.

I'm not sure if there will be any perl 6 diagnostics for packages classes in the wrong file, though, as I had suggested to the OP.

That is one way to look at it. I think it is more accurate to view it this way:
1. The first package specific_name statement creates a namespace and enters it.
2. Subsequent invocations simply reenter the namespace.
Having had the challenge of trying to explain the difference between C declarations and definitions to newbies; I can see how losing the distinction in dwimery would appeal as design choice for a higher level language.

My reply above to tanktalus gives more of my reason to view it this way.

Be well,
rir

1. The first package specific_name statement creates a namespace and enters it.
2. Subsequent invocations simply reenter the namespace.

While you may view that as conceptually accurate, that is not really what happens, hence my confusion above. I don't think I've ever come across this being an issue, not least because I would imagine that if you called code on a class you thought had declared, when in fact you had redeclared an existing class, something would break rather loudly.

I can't think of any obvious way to do this within perl, but as you say, it would probably fairly simple just to hack the perl source and recompile.

HTH

_________
broquaint

*Why* would it be good to have the package statement warn if the symbol table for that package already exists?

Just for grins, I have discerned that the package statement, by itself, appears to cause $::{<package>::} to spring into existence, so that is what you'd be looking for...but I don't see any general value in attempting to make repeated use of 'package X' warnable. In fact, switching the default namespace on the fly is a perfectly valid technique.

do other people see value in such a constraint?

Update: Bah. Ignore me. Misread the original node.

I'd still ask whether multiple declarations of the same package have been causing problems? Personally I cannot recall an instance of this causing problems so would question the utility of such warnings.

Phil