At Sun, 20 Jun 2010 16:21:14 +0200, Thomas Klimpel wrote:
[1 <text/plain; us-ascii (quoted-printable)>] David Abrahams wrote:
Stefan Strasser wrote:
I am wondering if there is any reason to avoid default arguments in general purpose libraries ?
this case won't compile, template arguments are not deduced from default arguments.
A problem, incidentally, that can be solved using Boost.Parameter.
It depends, especially if "perfect forwarding" (see [1] why I use "...") of some parameters is also required.
Boost.Parameter does a very good approximation of perfect forwarding, generating T&/T const& parameters for all out- and in/out- parameters. It does erase rvalue-ness, but that's pretty much a given with C++03 that AFAICT nobody knows how to avoid.
[1] It's not really about "perfect forwarding", but about capturing the non-const rvalue references. This is required for handling calls using adapters like "lapack::syev(bindings::lower(A), w);".
I'm just curious, Have you thought about using const rvalues as return types in these situations? If you consider the adapter itself to be immutable and the target sequence to be a separate object (which in reality it is), it actually all makes sense. And a T const return type will bind nicely to a generalized U& argument. Cheers, -- Dave Abrahams BoostPro Computing http://www.boostpro.com