Subject: Re: [boost] [result_of] Test fails on clang trunk and gcc-4.7 due to changes in FDIS
From: Michel Morin (mimomorin_at_[hidden])
Date: 2012-03-30 11:35:26
Eric Niebler wrote:
>>> Specifically, the change is about how decltype of a function call expression
>>> is determined.
>>> * N3242 says that in 18.104.22.168 p4:
>>> if e is a function call or an invocation of an overloaded operator
>>> (parentheses around e are ignored), decltype(e) is the return type
>>> of the statically chosen function;
>>> * N3290 (FDIS) does not have such a wording. For a function call expression,
>>> decltype(e) is determined by the last rule in 22.214.171.124 p4:
>>> otherwise, decltype(e) is the type of e.
> Right. I spoke with James Widman about this. He says the change was not
> because of the decltype v1.1 change, but rather about fixing core core
> issue 1212:
Thanks for providing the information!
I understand why the rule for xvalues is added,
but I don't understand why the rule for function calls is removed.
This removal is a breaking change...
> James Widman also agrees with your analysis. I guess the result_of tests
> are wrong then.
To accommodate both N3290 (FDIS) decltype and pre-N3290 decltype,
we need to modify the failed tests to something like this:
typedef const int F();
Or, should decltype-based boost::result_of emulate N3290 decltype
even on a compiler with pre-N3290 decltype?
Also, the implementation needs to be modified.
The current implementation of decltype-based boost::result_of
does not use decltype for function pointers.
So, for "typedef const int F();"
* boost::result_of<F&()>::type is int,
* boost::result_of<F*()>::type is const int,
on a compiler with N3290 decltype.
> Could you file a bug?
OK, I will file a bug later.
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