Use aggregate initialization instead of default initialization that l…

[tanmoy87544]

…eaves simple types undefined. The problem with the default initialization is it calls value initialization, which leaves simple types undefined. This gives a compilation error when Block(0) is being moved. Changing it to aggregate initialization forces elements to be zero initialized. The time penalty of constructing the arr_ array should be minimal.

[emstoudenmire]

Hi, so for this one, is the issue that it could give a compilation error in the future?

[tanmoy87544]

Hi, so for this one, is the issue that it could give a compilation error in the future?

Definitely with C++20, which is my default. But, the same standards violation (moving undefined parts of a struct) is true for C++17, I can check whether the compiler complains in C++17 mode or not.

[tanmoy87544]

Hi, so for this one, is the issue that it could give a compilation error in the future?

OK, checked. It complains when building v3 with g++ (MacPorts gcc10 10.2.0_5) 10.2.0

Compiling itensor/itdata/qdense.cc with optimizations
In file included from /Users/tanmoy/iTensor/ITensor/itensor/tensor/types.h:21,
from /Users/tanmoy/iTensor/ITensor/itensor/tensor/rangeiter.h:20,
from /Users/tanmoy/iTensor/ITensor/itensor/tensor/teniter.h:19,
from /Users/tanmoy/iTensor/ITensor/itensor/tensor/ten.h:20,
from /Users/tanmoy/iTensor/ITensor/itensor/tensor/sliceten.h:20,
from itdata/qdense.cc:20:
/Users/tanmoy/iTensor/ITensor/itensor/util/infarray.h: In member function 'std::tuple<const T*, itensor::InfArray<long int, 11>, long int> itensor::QDense::getEltBlockOffset(const itensor::IndexSet&, const Indexable&) const [with Indexable = itensor::InfArray<long int, 11>; T = double]':
/Users/tanmoy/iTensor/ITensor/itensor/util/infarray.h:131:31: warning: '((void)& +16)' may be used uninitialized in this function [-Wmaybe-uninitialized]
131 | vec_(std::move(o.vec_))
| ^
/Users/tanmoy/iTensor/ITensor/itensor/util/infarray.h: In member function 'std::tuple<const T*, itensor::InfArray<long int, 11>, long int> itensor::QDense::getEltBlockOffset(const itensor::IndexSet&, const Indexable&) const [with Indexable = itensor::InfArray<long int, 11>; T = std::complex]':
/Users/tanmoy/iTensor/ITensor/itensor/util/infarray.h:131:31: warning: '((void)& +16)' may be used uninitialized in this function [-Wmaybe-uninitialized]
131 | vec_(std::move(o.vec_))
| ^