Fixed and Nested Arrays

A small grid has a known shape. Nucleus records that shape in its type, so the compiler and runtime can check every selection without a heap or a hidden descriptor.

var grid as u8[3][2] = [[1, 2], [3, 4], [5, 6]]

This is an array of three elements. Each element is an array of two u8 values. Read the suffixes from left to right: grid[row] selects one u8[2] row, and grid[row][column] selects one byte in that row.

Length belongs to each level

Every concrete array and open array view has a read-only u16 .length. grid.length is 3, while grid[0].length is 2. This makes traversal follow the declared shape:

for row = 0 until grid.length
    for column = 0 until grid[row].length
        observed = observed + u16(grid[row][column])
    end
end

until is a natural match for zero-based indexing because the bound itself is the first invalid index.

Bounds and layout

Every index is checked against the selected array level. A negative signed index fails before the upper-bound check. An out-of-range access is a safety trap and cannot read or write the neighbouring object.

Nested arrays use row-major storage. The rightmost dimension is contiguous, so the six bytes in the example are laid out as the first row, second row, then third row. Selecting a row uses that row type's complete extent as the stride. The source still deals in arrays and indexes; it never sees a byte address.

The companion sums all six cells and leaves observed equal to 21.

var grid as u8[3][2] = [[1, 2], [3, 4], [5, 6]]
var observed as u16 = 0

sub main()
    var row as u16
    var column as u16

    for row = 0 until grid.length
        for column = 0 until grid[row].length
            observed = observed + u16(grid[row][column])
        end
    end
end

Summary

• T[N] is a fixed array with N elements.
• Array suffixes may nest to any admitted finite type depth.
• Each array level has its own read-only u16 .length.
• Indexing is zero-based and checked.
• Nested arrays use row-major layout.

See types and storage. The checked companion is 06-arrays.nu.