[Rcpp-devel] Sugar: This is not just a windows issue (partial fix): was sugar under Windows/g++ (MinGW) odd behavior.

[Dominick Samperi]

On Tue, Jan 25, 2011 at 3:23 AM, Romain Francois
<romain at r-enthusiasts.com> wrote:
> I'll have a look at this when I get a chance.

Obviously my proposed "partial fix" is really not satisfactory because it would
involve a lot of vector copying, defeating the purpose of expression templates.

The real issue is that the way Rcpp::Fast is defined results in
temporary creation
in the construction of Plus_Vector_Vector and friends, and to fix this
Rcpp::Fast
would have to be redesigned (by inheriting from Vector perhaps).

Until this happens the code that is conditionally ifdef-ed out when
IS_GCC_450_OR_LATER is defined should probably be unconditionally
ifdef-ed out.

Dominick

>
> Romain
>
> Le 25/01/11 02:58, Dominick Samperi a écrit :
>>
>> I reported a problem in another thread that I thought only surfaced
>> under Windows,
>> but I was wrong (see Subject line). The problem also appears under GCC
>> 4.5+,
>> and it appears that somebody already noticed problems with this version of
>> GCC
>> and introduced the compiler define IS_GCC_450_OR_LATER to navigate
>> around the problematic code.
>>
>> After some debugging, and based on the links that I posted in the original
>> thread, the problem seems to be due to the more recent versions of the
>> compilers GCC 4.5+ and VC++ 2010 introducing support for new reference
>> features that will not become official until C++0x is released later
>> this year (or in 2012).
>>
>> A partial fix that enables my test drivers to work is to replace
>> reference variables by non-references variables in constructors like
>> Plus_Vector_Vector. Specifically, the declarations
>>
>> const LHS_EXT&  lhs;
>> const RHS_EXT&  rhs;
>>
>> should be replaced with
>>
>> const LHS_EXT lhs;
>> const RHS_EXT rhs;
>>
>> This is a partial fix because I have not checked that this doesn't cause
>> other problems with expression evaluation, but it is a start...
>>
>> The problem with the original code is that the references lhs and rhs
>> are initialized to point to a temporary that disappears when the
>> constructor exits. This work-around simply saves a copy instead of
>> saving a reference.
>>
>> Dominick
>
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> Romain Francois
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