OCL25 — Multi-dimensional sortedBy

The sortedBy iteration provides an elegant solution to a sort problem in which the sort metric is a projection of the sorted object. Thus sortedBy(p|p.name) or just sortedBy(name) is short and avoids the opportunities for typos from a more conventional exposition involving comparison of two objects. The natural solution may well be an efficient one for large collections with non-trivial metrics.

However the sortedBy solution is unfamiliar and so confusing for newcomers and unsuitable for multi-key sorting for which an artificial compound single key may need to be constructed.

One solution might be to provide a more conventional iterator such as sort(p1, p2 | comparison-expression) allowing a two key sort:

sort(p1, p2 | let diff1 = p1.key1.compareTo(p2.key1) in
if diff1 <> 0 the diff 1 else p1.key2.compareTo(p2.key2) endif)

However this has poor readability and ample opportunities for typos.

Alternatively sortedBy with a Tuple-valued metric might support multiple keys as:

sortedBy(Tuple

)

(The alphabetical order of the Tuple part names determines the priority.)

(Since sortedBy is declaratively clear and compact, inefficient small/trivial implementations can be optimized to their sort() equivalents.)