[SOLVED] in perl how to write to caller's variable without using XS?

in perl how to write to caller's variable without using XS?

I'm writing unit tests around some old code, and find the need to write a mock around Apache2::Request's read() method

my $r = Apache2::Request->new(...);

$r->read(my $buf, $len);

Is there a way to write a function in Perl to populate $buf? I'm pretty sure the only way to do that is from XS code with a **, but I thought I'd at least ask first.

Using Apache2::Request directly leads to this, hence my desire to mock it.

perl: symbol lookup error: .../APR/Request/Apache2/Apache2.so: 
undefined symbol: modperl_xs_sv2request_rec

Solution

In a Perl subroutine or method, parameters are passed via the @_ array. Elements in this array are aliases for the variables in the calling sub.

The common way of unpacking @_ is by making a copy like this:

my($self, $buf, $len) = @_;

So assigning to $buf in this case won't work because you've only modified your copy of the variable. But if you directly modify the value in @_ then that will affect the caller's variable:

$_[1] = 'some data';