FeatureScript Arrow Operator Improvements

Alex_Kempen

In August of last year, Onshape added support for a new syntax operator, the arrow operator (->). It allows users to chain FeatureScript arguments together by passing the argument on the left of the operator into the function on the right as the first argument. For example, the following two statements are equivalent:

const mateConnectorQuery = myQuery->qEntityType(EntityType.BODY)->qBodyType(BodyType.MATE_CONNECTOR);
const mateConnectorQuery = qBodyType(qEntityType(myQuery, EntityType.BODY), BodyType.MATE_CONNECTOR);

The arrow operator is obviously a great inclusion, but it can only can be used to pass arguments into the first (i.e. leftmost) argument of a function. Thus, the arrow operator is not useful for functions like evaluateQuery and toWorld since the part of the argument which tends to change or be calculated in-line is the second argument rather than the first:

evaluateQuery(context, query);
toWorld(cSys, pointInCSys);

Thus, I propose the addition of a variant of the arrow operator which allows passing the argument into a function as the second argument of a function instead of the first. A logical form for this new operator would be a double arrow, either (-->) or (->>). The addition of this operator would thus enable the following statements:

if (evaluateQuery(context, myQuery->qEntityType(EntityType.BODY)->qBodyType(BodyType.MATE_CONNECTOR)) != [])// checks if query contains a mate connector
if (myQuery->qEntityType(EntityType.BODY)->qBodyType(BodyType.MATE_CONNECTOR)->>evaluateQuery(context) != [])

// projects a point onto a plane
const projectedPoint = evVertexPoint(context, { "vertex" : myVertexQuery })->>project(myPlane);
const projectedPoint = project(myPlane, evVertexPoint(context, { "vertex" : myVertexQuery }));

// turns the first sketchpoint of a sketch into a world point
const worldPoint = qCreatedBy(context, id + "mySketch", EntityType.VERTEX)->qNthElement(0)->>planeToWorld(sketchPlane);
const worldPoint = planeToWorld(sketchPlane, qCreatedBy(context, id + "mySketch", EntityType.VERTEX)->qNthElement(0));

This would enhance FeatureScript by making it easier to use certain functions in-line with each other and thus make code easier to write, understand, and troubleshoot.

For the sake of being thorough, here's a list of some commonly used functions which I believe would benefit from the addition of this operator:

evaluateQuery(context, query);
debug(context, value);
addDebugEntities(context, entities);
addDebugPoint(context, point);
toWorld(cSys, pointInCSys);
fromWorld(cSys, worldPoint);
project(plane, point);
getVariable(context, name);
planeToWorld(plane, planePoint);
worldToPlane3D(plane, worldPoint);
worldToPlane(plane, worldPoint);
scaleUniformly(scale, pointToScaleAbout);
lastModifyingOperationId(context, query);
startTracking(context, subQuery);
makeRobustQuery(context, subQuery);
makeRobustQueriesBatched(context, subQuery);
adjustAngle(context, angle);
constructPath(context, edgesQuery);
evPathLength(context, path);
isClosed(context, edge);
extractDirection(context, entity);

konstantin_shiriazdanov

There was a conversation about operator form of function chaining: https://forum.onshape.com/discussion/7621/operator-form-queries

And for this particular realization of arrow chaining I like more the idea to simply denote substituted argument by some special symbol as Ilya proposed:

b -> methodCall(a, ^, c);
 /*as equvalent for*/ 
methodCall(a, b, c);