"Andreas Pokorny" wrote
Hi,
"Andy Little" wrote
"Joel de Guzman" wrote
IIUC, the "rule" specifies the result type (not deduces the result type). I think it's not a macro at all; it would rather be something like: "unspecified_type", or "you-define-your-type-here-and-ill-do-the-rest"
Well again I am probably not understanding it fully, but from one of Andreas posts higher in the thread:
get_result_type<add_tag,LeftT,RightT>
presumably could be implemented as:
template <typename LeftT, typename RightT> struct get_result_type<add_tag,LeftT,RightT> { typedef BOOST_TYPEOF_TPL(LeftT() + RightT()) type; };
That would be a hen-egg situation. The result_type of the operator is defined by the rules, not the other way around. Like the Joel said, the encoding of the expression tree into operator and function return types is up to the user.
So the user must create special types solely for the purposes of the framework? cant I use the E.T engine on (say) 2 int's: int a,b; ETexpression_< ETexpression_<int>, plus_tag, ETexpression_<int>
::result_type result = ETexpression(a) + ETexpression(b);
regards Andy Little