Reusable Objects

Most features in FluidCAD consume their inputs. When you extrude() a sketch, the sketch geometry is removed from the scene so it can't accidentally be picked up by the next feature. The same applies to selections used by shell(), cut(), sweep(), and so on.

Calling .reusable() on an object tells FluidCAD to keep that object alive, so a later feature can use it again.

Extruding parts of a sketch at different heights

A common use case is drawing several shapes in one sketch and extruding each to its own height. Each geometry inside a sketch() is its own object, so you can mark some of them .reusable() and consume them one at a time:

import { sketch, circle, extrude } from 'fluidcad/core';

sketch("xy", () => {
    circle(100);
    circle(50).reusable();
});

extrude();

extrude(50);

The first extrude() picks up the 100-unit circle and pushes it to the default height. The 50-unit circle survives because it's marked reusable, so the next extrude(50) finds it waiting on the same sketch and extrudes it to 50 units. Without .reusable(), the first extrude() would consume both circles and the second call would have nothing to work with.

Reusing a whole sketch

You can also mark an entire sketch as reusable. This is useful when the same profile drives more than one feature — for example, extruding the same outline at two different heights without redrawing it:

import { sketch, circle, extrude } from 'fluidcad/core';

sketch("xy", () => {
    circle(60)
}).reusable();

extrude(20);

extrude(50);

extrude() always picks up the most recent sketch, so you don't need to keep a reference — marking the sketch reusable is enough to keep it around for the next call.

Cleaning up with remove()

A reusable object stays in the scene until you explicitly dispose of it. If you need to clean one up before later operations pick it up by accident, keep a reference and call remove():

const profile = sketch("xy", () => {
    circle(60)
}).reusable();

extrude(20);
extrude(50);

remove(profile);

Without this, a reusable sketch or selection can leak into later operations and cause unexpected results.

Where .reusable() applies

.reusable() works on any scene object whose shapes would otherwise be consumed:

• Sketch geometries — individual shapes inside a sketch() block
• Whole sketches — the object returned by sketch(...)
• Selections — the object returned by select(...), when the same selection drives multiple features (e.g. a sketch plane and a project() source)

tip

If you find yourself re-selecting or re-sketching the same thing twice in a row, that's usually a sign to mark the first one .reusable() and pass it to both features instead.