Re^3: eval "require $class" seems wrong

I was kinda suggesting the best practice was to avoid requireing dynamic class names completely, and address the problem at a higher level.

To answer your question directly, one can require either a class supplied as a bareword or a path. There isn't a way to require a class supplied in a scalar. In order to load a dynamically constructed class name, some use eval EXPR to do the former (e.g. Module::Pluggable), and some transform the class name into a path and use the latter (e.g. if). I have no idea why one cannot do require $class;.

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Re^4: eval "require $class" seems wrong by sgt (Deacon) on Aug 22, 2007 at 20:02 UTC
The second paragraph summarizes nicely the whole thread, but I cannot agree with the best practice you are suggesting which is don't use it IIUC. eval-require is a common idiom for conditional loading of modules and there is a need for that. From a language perspective a special "use" would be better like 'use any LIST' as the intent would be much clearer. Still you don't want "use base/use parent" wars^Wdiscussions for something simply expressed in an idiomatic but inelegant way. In the end I think low-level things like these should be made core pragmas and (possibly) written in C, thriving for a minimalistic implementation. cheers --stephan	[reply]
Re^5: eval "require $class" seems wrong by ikegami (Patriarch) on Aug 22, 2007 at 20:12 UTC
eval-require is a common idiom for conditional loading of modules and there is a need for that. No, you don't need either `eval` functions to conditionally load a module. `if (condition) { require Foo::Bar; }` [download] And you don't need `eval EXPR`* to do exception handling. `eval { require Foo::Bar; }; if ($@) { require Foo::Baz; }` [download] You only need `eval EXPR` to load a module whose name is not known at compile-time. The only things I can think of that fits that description are plugins/drivers, things well served by high-level modules. Do you have an example that requires `require $class` other than plugins/drivers? * — Remember, nothing wrong with `eval BLOCK` (called `try` in some other languages). Unlike `eval EXPR`, it doesn't invoke the Perl compiler. That means it doesn't incure a huge speed penalty and it doesn't require careful escaping and validation its argument.	[reply] [d/l] [select]
Re^6: eval "require $class" seems wrong by rvosa (Curate) on Aug 22, 2007 at 22:40 UTC
My question was exactly about plugins/drivers, i.e. I'm working on a code base that does dynamic loading of plugins, and find my self having to write eval "require $class" because of that. I can't really think of many other cases either (perhaps a factory?).	[reply]
Re^6: eval "require $class" seems wrong by sgt (Deacon) on Aug 23, 2007 at 09:20 UTC
still if you need a loop to pick up the first module to load of a list of modules (e.g say Math::Pari, GMP and other math libs). I am lazy and I don't want to write a require line for each one, or maybe I want to read my optional modules directly from the .yml shipped with the module etc... cheers --stephan	[reply]