At them moment it is not possible to define a rectangular array by the distance between each repeated instance. It would ideal if one could do this this for each axis. This would be incredibly useful as at the moment if I want an array of as many possible copies of an object that fits within a certain area with a certain separation, I have to manually calculate the extent of the largest array that will fit within that area with said separation.
For radial arrays, as far as I can work out, there is the similar issue that it is not possible either to define an array by the distance or, more usefully, by degrees of separation between each repeated instance. The UI seems to display the separation distance for radial arrays, and it is possible to give numerical input, but said input does not have any effect on the subsequent array. Similarly to rectangular arrays, currently, if I want a radial array of as many copies of an object that fits within a certain number of degrees along an certain arc with a certain angular separation, I have to manually calculate the angular extent of the largest array that will fit within the arc with said separation.
Adding separation distance to curve arrays is also conceivable, but I am sure there would be multiple ways to do this.