Use cases for hooks in @INC?

[LanX]

Perl has a powerful feature to include hooks in @INC. (see require for details)

These are basically callbacks which can install dynamically generated modules instead of reading the file system.

I'd be curious about typical use cases for this feature or know projects which apply this technique.

[belden]

One use is to observe the dependency graph of your codebase. You can do some things with an @INC hook that you can't do by overloading CORE::GLOBAL::require.

One of the things you can do with an @INC hook is signal the interpreter to keep looking for a file on disk, or fake out that you've got a module that you don't really have.

I've found that most of the time I want my @INC hooks to live at $INC[0] or at $INC-1, depending on whether I'm writing an observer or a fallback hook. Simply unshifting (or pushing) your hook where you want it isn't sufficient, since other modules you load can and will tamper with the ordering of things in @INC. "use lib", for example, will push to @INC, and if your hook depends on being the last most entry in @INC, then now you're broken. Tieing @INC is the only way I've found to ensure my hooks stay where I think they belong.

I wrote Array::Sticky::INC to ensure @INC hooks stay where they belong; you might have a look at that module, and some of the documentation I wrote up as part of it, for a bit more detail and use cases.

[Discipulus]

for completness i'd add How to use @INC coderef hooks

L*

[Anonymous Monk]

PAR, Portable, Re: how to make lexical pragma global, hints ( pl_hints $^H %^H ), taint::all (package taintall)

@INC.*\\& · CPAN->grep -> lib::http, Module::AutoLoad, persona

use.lib.*\\& · CPAN->grep -> Devel::Hide

So the basic use case is the same as for Filter::Simple

[LanX]

Thanks, cpan-grep is a clever approach.

Using the word hook instead of \\& gives additional hits.

> So the basic use case is the same as for Filter::Simple

Altering existing modules is one use case.

Another is loading existing modules from other sources like usb-sticks or via http.

I wonder if there is a use case where a module's source is generated on the fly.

[polettix]

Probably in the same ballpark as PAR, you can find an example at work here: I use it so that I can embed the full text of a module in a script, and load it dynamically. I guess FatPacker does something similar too.