Arrays

An array expands a joint into a distributed run of one part. It is how you get eighteen slats from one declaration, with the count computed rather than counted.

- id: slats_to_cleats
  kind: butt
  removable: true
  array:
    of: slat
    count: ceil((slat_cleat.blank.length - slat.blank.width) / (slat.blank.width + max_slat_gap)) + 1
    distribute: even
    span: [slat_cleat@left:face.start, slat_cleat@left:face.end]
  mate:
    a: slat:face.bottom
    b: slat_cleat@left:face.left
    align:
      contact: true
      roll: 180
      offset: [-slat_centre_offset, 0, 0]

Key
of	required	The part id to repeat.
count	required	How many. An expression.
span		Two anchor paths bounding the run.
distribute		even or even_gaps.
spacing		A fixed centre-to-centre distance, instead of a span.

span plus distribute, or spacing

span + distribute fills a run between two anchors. Use it when the ends are fixed and the spacing should fall out — slats between the ends of a cleat, shelves between the top and bottom of a carcass.

• even spaces the parts’ centres evenly across the span.
• even_gaps makes the clear gaps between them equal, which is what you want when the parts have width and the gap is the thing being checked.

spacing sets a fixed centre-to-centre distance and lets the run end where it ends. Use it when the pitch is what matters — shelf pins on the 32 mm system, balusters at a required maximum gap.

Compute the count; do not count it

count: ceil((slat_cleat.blank.length - slat.blank.width) / (slat.blank.width + max_slat_gap)) + 1

That expression reads: divide the run by one slat plus one maximum gap, round up, add the slat at the far end. Because max_slat_gap is derived from standards.bed.slat_gap_max, and the cleat length is derived from the mattress, changing us-queen to uk-super-king adds slats by itself and the gap stays legal.

Typing count: 18 is the version that is wrong the moment anything else moves. It is also the version that quietly stops satisfying the standard it was sized against, with nothing to say so.

The mate is written once, for one part

Inside an array, the mate is written as though there were a single part. The expansion applies it to each copy in turn and slides them along the span.

mate:
  a: slat:face.bottom
  b: slat_cleat@left:face.left
  align:
    contact: true
    roll: 180
    offset: [-slat_centre_offset, 0, 0]

That offset slides each slat from the left cleat across to the bed’s centre line, so it lands on both cleats rather than hanging off one. It is derived, like everything else, so it follows the mattress size.

Arrays or instances?

Use	When
instances	Two or three copies that sit in different, named places — a left post and a right post.
array	Many interchangeable copies in a regular run — slats, shelves, pickets.

Instances are placed by their own joints, one per copy. An array is placed by one joint, and its count can be an expression. If you are about to write instances: [a, b, c, d, e, f], write an array instead.

What the validator does with it

Two things worth knowing.

Findings are collapsed. If every slat in a run has the same problem, the report says so once with the count and the full subject list, rather than eighteen times. Twelve copies of one problem crowd out the other eleven problems in a context window.

The gap is checked against the standard, not against your arithmetic. DOM- findings read standards.bed.slat_gap_max directly. If the computed count leaves a gap of 78 mm, the report gives you the count that would not — with the number in it, ready to paste back.