Array / AsyncArray design

[d-v-b]

The Array and Group classes have methods that are synchronous, but many of these methods rely on async code. To solve this problem, the Array and Group classes have _async_array and _async_group attributes respectively. To use Array as an example, the Array._async_array attribute is an AsyncArray that actually does all of the IO, and so many Array methods just wrap a synchronized invocation of the corresponding AsyncArray invocation.

An alternative would be a single class with a mix of sync and async methods, where the sync form invokes the async form within a blocking function.

My question for this issue is whether we like our current design with two classes. Do people find it intuitive, etc?

I'm not arguing for changing anything, but I will note that I experience a mild distaste when I look up the implementation of an array method and find that it's actually just wrapping a method defined in a completely different class, which I must then look up to figure out what's really going on. The Array class has just 1 attribute, _async_array, which does all the work.

I'm not aware of a "synchronized layer above async layer" solution that doesn't involve extensive wrapping (if someone knows of one please share it!), but from a discoverability standpoint, Array._get_selection wrapping Array._a_get_selection seems a bit better than Array._get_selection wrapping AsyncArray._get_selection, especially if, in the first case, the sync and async methods are defined right next to each other in the source code.