How to use property validation functions in class definitions for struct fields?

Hi,

I have a class in which I define a struct S. How can I validate that its fields (c1, c2, ...) are numeric? mustBeNumeric or mustBeUnderlyingType(S,"double") throw an error because they checks if S itself is numeric/double.

classdef myClass
    properties
        a {mustBeText} = ''
        b {mustBeNumeric} = 0
        S { ? } = struct('c1',0,'c2',0,'c3',0)
    end
end

Thanks.

Answer 1

[chicken vector]

If this is helpful, please remember to vote for best answer.

You can read this for more info.

classdef myClass
    properties
        a {mustBeText} = ''
        b {mustBeNumeric} = 0
        S {mustBeStructWith3NumericFields(S)} = struct('c1',0,'c2',0,'c3',0)
    end
end

function mustBeStructWith3NumericFields(var)
if ~isstruct(var)
    error("Input must be a struct.")
end
fn = fieldnames(var);
Nfn = length(fn);
if Nfn ~= 3
    error("Input struct must have 3 fields.")
end
for j = 1 : Nfn
    if ~isnumeric(var.(fn{j}))
        error("Input struct fields must be numeric.")
    end
end
end

You can run the following to test that your validator function performes its task correctly:

a = myClass;

S = struct('a',1,'b',2,'c',3);
a.S = S;

S = ["a" "b" "c"];
try
    a.S = S;
catch ME
    fprintf(ME.message + "\n");
end

S = struct('a',1,'b',2,'c',3,'d',4);
try
    a.S = S;
catch ME
    fprintf(ME.message + "\n");
end

S = struct('a',"1",'b',2,'c',3);
try
    a.S = S;
catch ME
    fprintf(ME.message + "\n");
end

[Stephen23]

Note that IF-ERROR can often be simplified using ASSERT, e.g.:

function mustBeStructWith3NumericFields(var)
assert(isstruct(var), "Input must be a struct.")
fn = fieldnames(var);
Nfn = length(fn);
assert(Nfn==3, "Input struct must have 3 fields.")

etc.

[Davide]

Thanks! This is perfect