Suggestion to solve the problem that variable is empty due to fix in #34

[Hell3000]

Suggestion to solve the problem that not empty string variables are saved empty due to fix in #34
:
Added the elseif with the matlab version check in savejson.m.

function txt=obj2json(name,item,level,varargin)

if(iscell(item))
    txt=cell2json(name,item,level,varargin{:});
elseif(isstruct(item))
    txt=struct2json(name,item,level,varargin{:});
elseif(ischar(item))
    txt=str2json(name,item,level,varargin{:});
elseif ~verLessThan('matlab','9.1') && isstring(item)
    % versions 2016b (9.1) and higher AND item is a string object
    % version check is necessary because function isstring existst only since 2016b

    % There's a new string class with " " syntax since 2016b (9.1) with the following characteristic:
    % isobject("String") returns true
    % isstring("String") returns true
    % ischar("String") returns false
    %
    % vs. character arrays with ' ' syntax:
    % isobject('chararr') returns false
    % isstring('chararr') returns false
    % ischar('chararr') returns true

    % Don't know if this is correct in every case:
    % convert string to char by: item{:}
    txt=str2json(name,item{:},level,varargin{:});
elseif(isobject(item)) 
    txt=matlabobject2json(name,item,level,varargin{:});
else
    txt=mat2json(name,item,level,varargin{:});
end

I didn't test with 2016b. Only with 2014b and 2017a

[fangq]

thanks @Hell3000 for the detailed comments and patch. Because octave does not have function verLessThan, so I used the isa(..,'string') to tell if the string belongs to the new class.

I tested the failed samples raised in #34, #39 and #44, now savejson works without omitting fields. Feel free to reopen if this remains an issue.

>> a=struct(); a.b={string('hi')};
>> savejson('',a)

ans =

    '{
     	"b": [
     		"hi"
     	]
     }
     '

>> data = loadjson('{"Test": ["GML", "XML"]}')

data = 

  struct with fields:

    Test: {["GML"]  ["XML"]}

>> savejson('',data)

ans =

    '{
     	"Test": [
     		"GML",
     		"XML"
     	]
     }
     '