This segfaults currently because the call to method_int8_in tries to invoke the corresponding vfunc slot in the class struct for NoImplementation. But that's NULL since NoImplementation doesn't provide an implementation.
{ package NoImplementation; use Glib::Object::Subclass 'GI::Object'; }
{ my $foo = NoImplementation->new; local $@; eval { $foo->method_int8_in (23) }; like ($@, qr/method_int8_in/); }
To install Glib::Object::Introspection, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Glib::Object::Introspection
CPAN shell
perl -MCPAN -e shell install Glib::Object::Introspection
For more information on module installation, please visit the detailed CPAN module installation guide.