How can I write code that optionally uses a module if it exists? [duplicate]

问题

This question already has answers here:

How can I require an optional Perl module if installed? (8 answers)

Closed 2 months ago.

If I want to write code that optionally uses a module how can I do it? For example, if I want to write code that warns Dumping an object if Data::Dumper is available or otherwise just warns, how can I do that?

回答1:

BEGIN {
   if (eval { require Data::Dumper }) {
      *dumper = sub { warn(Data::Dumper::Dumper(@_)) };
   } else {
      *dumper = sub { };
   }
}

dumper(...);

---

The downside of the above is that expensive expressions passed as arguments still need to be calculated if Data::Dumper isn't available.

use constant has_dumper => eval { require Data::Dumper };

BEGIN {
   if (has_dump) {
      *dumper = sub { warn(Data::Dumper::Dumper(@_)) };
   } else {
      *dumper = sub { };
   }
}

dumper(...);                # Ok
dumper(...) if has_dumper;  # Statement completely optimized away if DD missing.

回答2:

This is an effective idiom for loading an optional module,

use constant has_Module => defined eval { require Module };

This will require the module if available, and store the status in a constant.

You can use this like,

use constant has_DataDumper => defined eval { require Data::Dumper };

warn "got object";
if ( has_DataDumper ) {
  warn Data::Dumper::Dumper( $obj );
}

来源：https://stackoverflow.com/questions/64918978/how-can-i-write-code-that-optionally-uses-a-module-if-it-exists