XRT-2602 add iot_data_iter

[dpazj]

We discussed a generic array type iterator. Some of my current work would benefit from this so came up with an example implementation. Some feedback would be good before I go any further. Hopefully you can get the gist from this.

iter_get_value() for an iot_data_array_t would return an iot_data_t that user can read, however they would not be able to modify the underlying array, unless there is a way you can create a ref to an numerical type?

[SteveOss]

Some WIP comments:

• Will need unit tests
• Would just call type iot_data_iter_t, just doc how it can be used. Assert if associated with wrong kind of data.
• Coding standards braces {} vertically align.
• Wouldn't bother with ARRAYKIND_ITER_SWITCH, actually makes code less readable.
• Would extend so also iterates maps

[dpazj]

@SteveOss ready for review

[dpazj]

@SteveOss For array support we could allocate an iot_data_t and require a user to call a function like iot_data_iter_clear once they have finished with the iter? Would be a bit inconsistent with other api usage, but would allow us to keep arrays.

[SteveOss]

@dpazj Even allocating an iot_data_t for an array iterator, doesn't work WRT to ownership when considering both lifetime of value and validity of scope, as essentially target collection type isn't holding iot_data. Also is pretty inefficient for iterating arrays of basic types. Not seeing a solution that works for array given existing iterator semantics.

[dpazj]

recheck

[dpazj]

@SteveOss CI seems to be stuck. Any ideas?