Idea: Accessing aspects of arrays of records directly

[zayenz]

Using records makes it clearer how data is structured in a model. However, in combination with many constraint being defined over arrays of aspects, it is easy to get into situations where there is a lot of boiler-plate. I think it might make sense to add the ability to access aspects of a record on an array of records.

As an example, consider this simple packing model using the no-overlap ("diffn") constraint

include "globals.mzn";


enum Boxes = B(1..10);
set of int: Pos = 1..100;

array[Boxes] of int: box_size = [20 | b in Boxes];

array[Boxes] of record(var Pos: x, var Pos: y): box;

constraint forall(b in Boxes) (
    box[b].x + box_size[b] in Pos /\
    box[b].y + box_size[b] in Pos
);

constraint diffn(array1d(Boxes, [box[b].x | b in Boxes]),
                 array1d(Boxes, [box[b].y | b in Boxes]),
                 box_size, 
                 box_size);

solve satisfy;

There is a lot of noise around writing the diffn-call. If we instead allowed box.x to represent a Boxes indexed array of var Pos, the constraint could be written like this

constraint diffn(box.x, box.y,
                 box_size, box_size);

With #968, the call would be less noisy, but having to do an array comprehension each time is still just busy-work.

[guidotack]

This is pretty high on the to-do list (and should be easy to do). You don't even need #968, because box.x will have the same index set as box, so no additional coercion will be required.