On 07/30/12 13:06, Larry Evans wrote:
http://steven_watanabe.users.sourceforge.net/type_erasure/libs/type_erasure/...
Specifies that the T... are placeholders; however, it doesn't specify that they be unique; hence,
tuple<concept,_a,_a> x(int(0),std::vector<int>(0));
would satisfy the current description but wouldn't be right. Of course no one would intentionally do that; however, if the Tags are calculated in some meta-program, it might happened accidentally. Hence the requires class should also say, "If T... are not unique, no diagnostic occurs", or something similar.
The reason I think "no diagnostic occurs" is that I've looked briefly in tuple.hpp, at the:
::boost::type_erasure::cons<Concept, T...> impl;
in the class tuple definition and the cons definition, and I don't see any check for duplicates.
Running the attached test, which includes a tuple with duplicate tags, produces no compile error; hence, I think putting: "no diagnostic occurs" in this case in the tuple docs is justified. I thought maybe mpl::map, which is used in tuple to create the bindings, would check for duplicates; however, the second attachment, with an mpl::map containing duplicate keys, compiles OK. -regards, Larry