Le 15/11/12 01:02, Darren Cook a écrit :
so when the object returns from this as, a copy is involved. We return a
T, not a T*, or a T&
I wonder if this gets optimized away, though? E.g.
http://blog.knatten.org/2011/08/26/dont-be-afraid-of-returning-by-value-know-the-return-value-optimization/
Definitely worth profiling and/or looking at the assembly before any
hard manual optimization.
Darren
Good point. Feel free to get started ;-)
Fuller quoting, for context:
This is complicated. For the moment I think copies are involved often.
But we have opportunities to recognize that we don't need to make copies.
For example :
void foo( const SomeClass& x ) ;
at the moment, in order to invoke the function, we essentially call :
as<SomeClass>
which goes down to :
/** handling T such that T is exposed by a module */
template <typename T> T as(SEXP x,
::Rcpp::traits::r_type_module_object_tag ){
T* obj = as_module_object<T>(x) ;
return *obj ;
}
so when the object returns from this as, a copy is involved. We return a
T, not a T*, or a T&
We might be able to identify that we want a reference. that is more work.
It is worth making a few tests with some dummy classes that prints on
copy constructor to see how many times it is used, etc ...
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