Re: ML incompatibility when concatenating objects of different classes

[Ben Abbott]

On Aug 7, 2011, at 5:54 PM, Ben Abbott wrote:

> On the help list a question came up on object precedence with concatenating 
> objects. Found very little information in either Octave's or Mathworks' 
> documentation, so I did some experimenting at the command line and found that 
> ML and Octave give different results.
> 
> I've identified seven groups of objects in ML. Objects within groups have 
> equal precedence.  Group (1/logical) has the lowest pecedence and group 
> (7/function_handle) has the highest precedence.
> 
> (1) logical
> (2) double
> (3) single
> (4) uint8, uint16, uint32, uint64, int8, int16, int32, int64
> (5) char
> (6) struct, cell
> (7) function_handle
> 
> Arrays of function handles are not allowed. Thus, they may be ignored  with 
> regards to precedence when concatenating objects.
> 
> If a cell is concatenated with other objects, of lower precedence, they are 
> each converted to cells. For example, the command below is valid ML syntax 
> and produces a cell array.
> 
> a = [{}, logical(1), double(1), single(1), uint32(1), 'a', 
> struct('foo','bar')]
> 
> ML gives the indicated results for the concatentations below 
> 
> class ([true, double(1)]) = "double"
> class ([double(1), single(1)]) = "single"
> class ([single(1), uint32(1)]) = "uint32"
> class ([uint32(1), 'a']) = "char"
> class (['a', cell(1)]) = "cell"
> class ([cell(1), struct('foo','bar')]) = "cell"
> 
> When concatenating objects of equal precedence, Octave and ML return an 
> object whos class  consistent with that of the fist object.
> 
> Octave is also consistent with ML when concatenating numeric and character 
> classes.
> 
> Concatenating matrices with cell arrays gives an error in Octave. For 
> example, using a trival character scalar ...
> 
> a = 'a';
> [a, cell(1)]
> error: invalid concatenation of cell array with matrix
> 
> [cell(1), a]
> error: concatenation operator not implemented for `cell' by `scalar' 
> operations
> 
> Structures and cells have equal precedence, and the example below should 
> produce a cell object.
> 
> [cell(1), struct('foo','bar')] 
> error: concatenation operator not implemented for `cell' by `scalar struct' 
> operations
> 
> But the one below should (and does) give an error.
> 
> [struct('foo','bar'), cell(1)] 
> error: concatenation operator not implemented for `struct' by `cell' 
> operations
> 
> I've opened a bug report, but thought I'd mention here in case it might be 
> important enough to fix prior to the next release.
> 
>       https://savannah.gnu.org/bugs/index.php?33966
> 
> Ben

I don't have a clue how to fix the parser, but I did prepare a changeset to add 
some tests to .test/test_parser.m

        https://savannah.gnu.org/patch/index.php?7592

The additional tests currently produce seven failures.

Ben