$ cat ./coderref
#!/usr/bin/perl

package CodeRef; 
{
    use Object::InsideOut;

  my @code :Field
           :Std( Name => 'code', Private => 1 )
           :Arg(Name => 'code', Mand =>1 )
           :Type(CODE_REF);

sub call() {
    my $self = shift;
    my $code = $self->get_code();
    return $code->(@_);
  }

}

1;

#=====
package main;

sub sum {
  my $sum =0 ;
  foreach my $num (@_) {
    $sum += $num;
}
  return $sum;
}

my $cref = CodeRef->new( code => \&sum );

$ ./coderef
OIO::Args error: Bad value for initializer 'code': CODE(0x9d16cc0)
Usage: Initializer 'code' for class 'CodeRef' must be an object or ref of type 'CODE_REF'
Package: main
File: coderef
Line: 35

Trace begun at coderef line 35