On 11 November 2012 15:34, Herbert Valerio Riedel <hvr@gnu.org> wrote:
> I'd argue that there is no harm in allowing this kind of compile-time
> conditional APIs using the DefaultSignature language extension.

I agree.

There's one minor issue: Say some client does not intend to rely on
DefaultSignatures but forgets to write a definition for the method. He
will then not get a "No explicit method or default declaration"
warning. However, in this case I think the benefits outweigh this
disadvantage.

FWIW I prefer that deepseq and hashable both use the DefaultSignatures
extension to provide generic default definitions.

hashable won't be using DefaultSignatures. See the discussion here:

https://github.com/tibbe/hashable/pull/33