Put and get packed arrays / matrices

[simonbyrne]

The main technical challenge is figuring out what is the element type of the array. This isn't documented, but see:

• https://groups.google.com/d/msg/comp.soft-sys.math.mathematica/tPim3jnfh9I/14rVRRZjM80J
• https://mathematica.stackexchange.com/questions/180706/how-to-send-packed-array-from-math-kernel-to-3rd-party-app-via-wstp

At the interface level, there are two main challenges:

• Mathematica is row-oriented instead of column-oriented
• Each dimension in Mathematica can have a "name" (typically List, but can be different).

So it would probably make sense to define a new type (WArrayExpr) to store these?