package Foo;
use warnings;
use warnings::register;
sub some_func{
   warnings::warnif("some_func");
   print "some_func() doesnt do much right now....\n";
}
package main;
no warnings;
Foo::some_func();
use warnings;
Foo::some_func();
__END__
some_func() doesnt do much right now....
some_func at C:\Temp\warnings.pl line 12
some_func() doesnt do much right now....