Adam,
This lead me on to the following, rather pedantic, musing on the provision of the identity[] directive in the core library to 'flatten' composed attributes. [snip] I wondered if providing identity[] for situations like these may result in more logical user code.
That sounds good to me. Would you be willing to contribute the identity[] directive? In this case we would need some docs, tests, and an example or two as well.
Yes no problem. The implementation was attached to my original mail but when I get the time I will have a look at adding some docs/tests/example also. I've been meaning to learn QuickBook for some time -- this may be just the excuse.
I was thinking more about your identity[] component and I realized that we actually don't need it. Spirit already has the special placeholder spirit::_0 which refers to the whole attribute of the expression the semantic action is attached to. So your code could be rewritten as: idxspec = '[' >> (start || (':' >> -start)) [ _val = access_index (_r1, lvalue, _0) ] >> ']'; where _0 refers to the whole tuple<optional<S>, optional<optional<S>>>. Sorry for not remembering this earlier... HTH Regards Hartmut --------------- Meet me at BoostCon www.boostcon.com