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Subject: [boost] [type_erasure]suggest tuple doc contain requires clause specifying T... are unique
From: Larry Evans (cppljevans_at_[hidden])
Date: 2012-07-30 14:06:12

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

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.


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