Use of std::cbegin causes problems with custom storage classes.

[shiozaki]

Recent changes by Ed breaks BAGEL. In short, that is because my custom storage class has a member function cbegin, but there is no std::cbegin(my_storage).

Yes I know there are cbegin(strorage) and storage.cbegin(), and the former is more fashionable these days in the light of C++11, but I believe introducing a new requirement for mere philosophy is a bad idea.

My suggestion is to use storage.begin() and to wait till std::cbegin is part of the standard.

[shiozaki]

The following is the error. The last version that worked with BAGEL was the one right after Telluride.

../../../btas/tensorview_iterator.h: In instantiation of 'const typename btas::TensorViewIterator<Range, Storage>::base_type::reference btas::TensorViewIterator<Range, Storage>::operator*() const [with Range = btas::RangeNd<(CBLAS_ORDER)102u>; Storage = const bagel::varray<double>; typename btas::TensorViewIterator<Range, Storage>::base_type::reference = const double&]':
../../../src/math/matrix_base.h:276:49:   required from 'void bagel::Matrix_base<DataType>::copy_block(int, int, int, int, btas::TensorView2<DataType>) [with DataType = double; btas::TensorView2<DataType> = btas::TensorView<double, btas::RangeNd<(CBLAS_ORDER)102u>, bagel::varray<double>, btas::TensorViewPolicy<(btas::TensorViewPolicy_ConstnessPolicy)1u> >]'
../../../src/math/matrix_base.cc:28:23:   required from here
../../../btas/tensorview_iterator.h:96:42: error: no matching function for call to 'cbegin(const bagel::varray<double>&)'
         return *(cbegin(storageref_.get()) + *iter_);

[shiozaki]

842b0a5 was the one that worked fine.

[shiozaki]

Even if I change that to storage.cbegin(), it does not compile (too many errors to assess...).
I guess there should be a test case that uses a custom storage class that is compliant with BTAS spec. Also see #50 that is still open and has not been addressed.

[evaleev]

@shiozaki this is leftover from trying to use T* as Storage ... did not work well (required reimplementation of reference_wrapper<T*> or metaprogramming).

In 02675d8 implemented std::cbegin/cend/other missing pieces if C++14 is not available. Your classes now should be usable. Please add a separate issue for the compilation errors.

[shiozaki]

Thanks. Also the recent changes seem to have fixed the compilation problem.