Cannot seem to save data to a file within a class

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I have a class which needs to write data to files. However, when I try to write the data, it gives a "variable not found" error, despite the variable being declared in the lines immediately preceding the call. I can manually run the code from the matlab command line and it does what I expect, so I think that the code is fine, but by being put into a class it somehow changes where the variables live. This is a shortened (working) version of what I have:
classdef SaveFiles < handle
function s = SaveFiles(loc)
s.fileLoc = loc;
function s = addData(s, data) = data;
function s = writeData(s)
data =;
evalin('base', sprintf('save(''%s'', ''data'')', s.fileLoc));
From the matlab command line:
>> sf = SaveFiles('<file_loc>');
>> a = 1;
>> sf.addData(a);
>> sf.writeData();
This last line causes the following exception:
Error using save
Variable 'data' not found.
Error in SaveFiles/writeData (line 18)
evalin('base', sprintf('save(''%s'', ''data'')', s.fileLoc));
I'm completely stumped. Is there something obvious I'm just overlooking?

Accepted Answer

per isakson
per isakson on 2 Mar 2018
Edited: per isakson on 2 Mar 2018
Yes, there is. To make it work, replace
evalin('base', sprintf('save(''%s'', ''data'')', s.fileLoc));
save( s.fileLoc, 'data' )
Why do you think you need to execute save in the base workspace? The variable data is not available in the base workspace, but in the workspace of the method.
Then there is a second issue. With handle objects, there is no need to return the object variable in methods, e.g. replace
function s = addData(s, data)
function addData(s, data)
However, the constructor shall return the object variable. See Comparison of Handle and Value Classes
per isakson
per isakson on 3 Mar 2018
"I "need" to return the object for consistency with the rest of the codebase" Fine, then you do it for a reason, not by mistake - which I suspected.

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