A range-of-columns accessor, symmetric with the row-range accessor

Cluster: address-decoding

Scenario

The worksheet API exposes a single-column accessor and a range-of-rows accessor, getting one row or a contiguous block of rows, but no symmetric range-of-columns accessor. Callers who want to operate on several adjacent columns at once must loop over single-column lookups and assemble the array themselves. A range-of-columns accessor would return a contiguous block of column objects in one call, mirroring the row-range accessor for symmetry and ergonomics.

Desired behavior

Provide a worksheet method that returns a contiguous run of column objects, symmetric with the existing method that returns a contiguous run of row objects. Given a start column and a count, or a start and end column, return the corresponding array of column accessors, each usable for setting width, hidden and numFmt and for per-cell access.

Prior art: the library already ships a single-column accessor, by index or letter, and a multi-row accessor that takes a start and a length and returns an array of row objects. The column accessor should follow the same shape so the two axes are consistent.

Open questions

• Signature: (start, count) against (firstCol, lastCol) Settled by precedent: first and last, inclusive. Worksheet.getRange takes (top, left, bottom, right) as inclusive corners in either order, and states that convention as binding on every range-shaped accessor here, so a columns accessor must be (firstCol, lastCol) and a rows one (firstRow, lastRow). One reading of a pair of numbers across all three axes, with no start-and-count overload beside it.
• Column identity: accept 1-based numeric indices, or letter references, consistently with the single-column accessor.
• Out-of-range or non-positive count: define whether an empty array, undefined, or an error is returned, and state it explicitly rather than inheriting the row accessor's behavior implicitly.
• Laziness: returned column objects should be the same lazily-materialized column objects the single accessor returns, so reading a range does not force allocation of empty columns.

Related note: worksheet-columns-mutable-array-ergonomics, since both concern making the column axis as ergonomic as the row axis.