Naming models

During the design process, we will add more geometry to our design. Therefore, it is useful to identify each sub-geometry by a name. In the next we want to give the rectangle a name outer, so we can identify it more easily:

outer = std::geo2d::Rect(width = 31.8mm, height = 15.8mm);

By adding outer = to the call std::geo2d::Rect(..), we have created an assignment. Now, the output rectangle will be stored in the value outer. However, when we export the file again via microcad export lego_brick.µcad, you will notice that nothing is exported.

Why? Because in µcad, assignments are not part of the output geometry. A second statement outer; is needed to output the geometry stored in the outer value.

outer = std::geo2d::Rect(width = 31.8mm, height = 15.8mm);
outer;

Naming the rectangles leads to some better readability but the code will get quite a bit longer, because for each rectangle we now need a second statement to render them.

This makes more sense, if you use an Operator (-) instead of an Operation (subtract()) to combine them.

use std::geo2d::Rect;

thickness = 1.2mm;
width = 31.8mm;
height = 15.8mm;

// name both rectangles
outer = Rect(width, height);
inner = Rect(width = width - 2 * thickness, height = height - 2 * thickness);

// what was { .. }.subtract() before:
outer - inner;

Now any reader can easily understand what's going on.

As you might have mentioned, we do not need the line use std::ops::subtract; anymore. This is because µcad brings some builtin binary operators which are hard-linked to builtin operations:

Those builtin operations are from the builtin library which can be found within the global module __builtin.

Usually there is no need to use the builtin library directly, because all builtin functionalities are also accessible via the standard library and with a more convenient interface.