On 03/02/08 20:19, Eric Niebler wrote:
Larry Evans wrote:
On 03/02/08 19:39, Eric Niebler wrote: [snip]
Your problem distills down to:
typedef terminal<x> GX; // grammar for x typedef GX::type EX; // expression for x
typedef shift_right<GX, GX> SRGX; // grammar for x>>x typedef SRGX::type SREX; // OOPS!
You then try to use SREX as a valid expression type, and it is not. It should be:
typedef shift_right<EX, EX>::type SREX;
The difference is that in the first case, you're creating the type of a right shift expression where the operands are grammars. You really want the operands to be expression types. [snip]
I'd be more comfortable if the validity of the nested type didn't depend on particular type of the template parameter.
It doesn't.
If the template arguments are grammars then shift_right<L,R>::type is not an expression type. AFAICT, it's of no use. OTOH, If the template arguments are expression types then shift_right<L,R>::type is an expression type, at least according to what you say above. So maybe I should have said the "usefulness" instead of "validity".