[RFC] How to implement stuff that makes sense only under certain conditions

[Torsten Förtsch <to...@gmx.net>]

Hi,

as you perhaps know I have recently added APR::Socket->fileno. But on Windows 
this function doesn't do anything useful.

Later I have added the C<#_if_ ...> mini language to ModPerl::MapUtil, see
http://svn.apache.org/viewvc?rev=940287&view=rev

The latter was caused to make modules like ModPerl::Interpreter possible that 
make sense only if perl has been compiled to support multiple interpreters.

See
http://svn.apache.org/viewvc/perl/modperl/branches/threading/xs/maps/modperl_structures.map?rev=940297&r1=940296&r2=940297&view=diff
http://svn.apache.org/viewvc/perl/modperl/branches/threading/xs/maps/modperl_types.map?rev=940297&r1=940296&r2=940297&view=diff

Now I think in cases like APR::Socket->fileno it might be better to leave it 
unimplemented when it cannot do anything useful. That would mean the user 
would see something like this in the error_log:

[Sat May 08 14:19:39 2010] [error] [client 127.0.0.1] Can't locate object 
method "fileno" via package "APR::Socket" at /home/r2/work/mp2/trunk/clean-
trunk-prefork/t/response/TestAPR/socket.pm line 43.\n

Now the user of a module that uses something that is not implemented under 
certain conditions can ask the author what that means instead of silently 
wondering what he did wrong.

My question in general is

* is it better to implement something like
  C<< return -1 if $^O eq 'win32'; do_the_real_stuff >>

* or leave it conditionally unimplemented like this:
Index: xs/maps/apr_functions.map
===================================================================
...
+#_if_ $^O ne 'linux'
  mpxs_APR__Socket_fileno | | apr_socket_t *:socket
+#_end_
...
+#_if_ $^O ne 'linux'
 ~apr_os_sock_get
+#_else_
+-apr_os_sock_get
+#_end_
...

Comments?

Torsten Förtsch

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