Compose with validateattributes

Hi,

Using a parser, I would like to check that the input is of a given class (say 'numeric'), with given attributes (say a vector with positive entries) and also fulfills some other constraints (say it sums up to 1)

This line: p.addParamValue('w',1,@(x)validateattributes(x,{'numeric'},{'positive','vector'}))&&(abs(sum(x)-1)<10^-6));

doesn't work (or no longer work?) as validateattributes doesn't output anything when correct.

Any solution? Thanks.

Answer 1

[Walter Roberson]

There is no known good way of using a sub-expression in an anonymous function when the subexpression does not return any value.

David Young came up with a hack during a recent Puzzler; to see the form of his solution to this trick, see here

Answer 2

[David Young]

I agree that validateattributes is not general enough - I remember hitting the same difficulty. You could perhaps use a function like the following - put it in your path and call it instead of validateattributes - though it's a shame that such a ruse is necessary:

function ok = checkattributes(a, classes, attributes)
%CHECKATTRIBUTES is like VALIDATEATTRIBUTES but returns true or false
%   OK = CHECKATTRIBUTES(A,CLASSES,ATTRIBUTES) takes the same arguments as
%   VALIDATEATTRIBUTES, excluding the three optional arguments. However
%   CHECKATTRIBUTES returns true or false when VALIDATEATTRIBUTES would
%   return or throw an exception respectively.
%
%   See also VALIDATEATTRIBUTES.

try
    validateattributes(a, classes, attributes, 'checkattributes');
    ok = true;
catch ME
    if ~isempty(strfind(ME.identifier, ':checkattributes:'))
        ok = false;  % first argument failed the specified tests
    else
        rethrow(ME); % there was some other error
    end
end
end

[ EDIT: Function changed to throw an error if there is something wrong with the arguments other than that the first one fails the required tests.]

Answer 3

[Teddy Furon]

Thanks Walter, Thanks David! I didn't miss anything: validateattributes is a pity and it needs a hack. Teddy

Answer 4

[Jiro Doke]

Considering that you require a workaround anyway, I might go with this for your specific case:

p.addParamValue('w',1, @(x) isnumeric(x) && all(x>0) && ...
                isvector(x) && (abs(sum(x)-1)<10^-6));