Re: [boost] [proto] subscript_wrapper and templated operator[]

Subject: Re: [boost] [proto] subscript_wrapper and templated operator[]
From: Eric Niebler (eric_at_[hidden])
Date: 2009-01-15 00:35:27

Eric Niebler wrote:
> David Deakins wrote:
>> While using proto with some classes that have a templated operator[] 
>> on VC8 and VC9, I have run into a '2 overloads have similar 
>> conversions' ambiguity error (C2666).  The problem seems to be with 
>> subscript_wrapper in detail/decltype.hpp, where neither the templated 
>> operator[] from the original class nor the fallback 'any 
>> operator[](any)' function in subscript_wrapper have priority.  Any 
>> thoughts on how to tweak subscript_wrapper so that the 'any 
>> operator[](any)' function looks like a worse match than the templated 
>> operator[] and thus prevents the ambiguity?  I attached a small test 
>> case that reproduces the problem. Also, for reference, I am using the 
>> proto code from the release branch as of a couple days ago (~12 Jan 
>> 2009).
> 
> I can reproduce this error with msvc but not with gcc. I think this may 
> be a msvc bug. Sadly, I don't know of a work-around. I'll give the issue 
> some thought.
> 
> Thanks for the report.

I've filed this bug with microsoft:
http://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=398868

I've also committed a work-around to trunk. If the test results look 
good, I should have this merged to release in time for 1.38.

Thanks,

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com