[C++] Add operator[] to some concrete Array implementations?

[asfimport]

I have occasionally been in situations where I want to pass in e.g. Int32Array or BooleanArray into a template that also can accept STL sequence types like std::vector<bool> – in such cases the main API of interest is []. Would there be interest in aliasing operator[] to return the result of GetView (or to deprecate GetView in favor of operator[])?

Reporter: Wes McKinney / @wesm
Assignee: Pradeep Garigipati / @9prady9

Related issues:

• [C++] Vendor forward compatible std::optional (is blocked by)

PRs and other links:

• GitHub Pull Request #11694

_{Note: This issue was originally created as ARROW-6276. Please see the migration documentation for further details.}

[asfimport]

Francois Saint-Jacques / @fsaintjacques:
I wanted such interface. I think we have to come up with a way to return option<T> and T depending on the null count, we could achieve this with a shim Array wrapper. I'd also like if we could have c++ iterators.

[asfimport]

Antoine Pitrou / @pitrou:
We now have STL iterators in arrow/stl_iterator.h for a couple datatypes (primitive, binary).
We could add syntactic sugar for indexed access, e.g.:

typename IteratorType::ValueType operator[](int64_t i) {
  return *IteratorType(*this, i);
}

[asfimport]

Pradeep Garigipati / @9prady9:
@wesm @pitrou Is the following kind of change that is intended ? or the operator overload should take a scalar of NumericType ?

bool BooleanArray::operator[](int64_t i) const { return GetView(i); }
value_type NumericArray::operator[](int64_t i) const { return GetView(i); }
TypeClass::DayMilliseconds DayTimeIntervalArray::operator[](int64_t i) const { return GetView(i); }
TypeClass::MonthDayNanos MonthDayNanoIntervalArray::operator[](int64_t i) const { return GetView(i); }

[asfimport]

Antoine Pitrou / @pitrou:
See my comment above. So, yes, it's this kind of change.

[asfimport]

Pradeep Garigipati / @9prady9:
The first two sentences of the original description kind of confused me (as in the operator[] indexes one Array using another Int32Array or something like that) even though the last sentence does say the new operator overload should return GetView's result.

Thank you for the clarification. I have raised the PR, please have a look.

[asfimport]

Eduardo Ponce / @edponce:
Now that Array types support {}operator[]{}, should it be used instead of GetView()? If so, then should we substitute all invocations to GetView() and make GetView() a private method which serves only as the implementation of operator[]?

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 11694
#11694