Questions ad marshalling multi-dimensional arrays

[Simon McVittie]

On Thu, 23 Jun 2011 at 14:33:37 +0200, rony wrote:
> On 23.06.2011 13:59, Simon McVittie wrote:
> > You can choose whether to use "row-major" or "column-major" ordering.
> > Whichever you do, document it as part of your API specification, preferably
> > with an example.
> >   
> Hmm, so there is no pre-determined ordering, independent of language or
> programming style when using multidimensional arrays?

As I said, there are no multi-dimensional arrays on D-Bus. If your language
has multi-dimensional arrays, it's up to you to turn them into arrays-of-arrays
or "stride-based" arrays.

> Was wondering in what sequences I should expect something like "aai" or
> "aaa(su{so})" got marshalled, such that unmarshalling would create an
> array with the same ordering as the sender.

Any D-Bus type has a well-defined ordering in the D-Bus wire protocol
(depth-first: if you have an array of arrays, the first inner array is
completely marshalled before you start on the second inner array).

However, multi-dimensional arrays are not a D-Bus type; D-Bus only has
(single-dimensional) arrays, aX for any type X. Because the type system is
recursive, X can itself be an array type, so you can have an array of
(arrays of ...) arrays, with a signature like aai.

aai unmarshals into an array of array of integer, which isn't the same thing
as a 2D array of integers. (Think "list of lists" in Python or Perl,
or List<List<Int>> in Java or C#, or whatever.) I would not recommend trying
to convert an array-of-arrays into a multi-dimensional array automatically
during unmarshalling, because an array-of-arrays isn't necessarily
rectangular/cuboid/hypercuboid/whatever higher dimension you're in.

    S