Question

I created this very useful bit of code to assign variables dynamically from a struct :

function getParam(param)
% this function extracts the fields of structure param and assigns them
% to variables of corresponding names in the caller workspace
allFieldsParam = fieldnames(param);
for iField = 1:length(allFieldsParam)
  assignin('caller',allFieldsParam{iField},param.(allFieldsParam{iField}));
end

The problem is that when I call getParam within a function, sometimes it works and sometimes it returns an error of the form :

??? Error using ==> assignin
Attempt to add "blocksizes" to a static workspace.
 See MATLAB Programming, Restrictions on Assigning to Variables
 for details.

    Error in ==> getParam at 7
      assignin('caller',allFieldsParam{iField},param.(allFieldsParam{iField}));

    Error in ==> classif_nmf_db at 15
    getParam(param);

Anyone has a clue how I can fix this ?

Regards
AL

Answer 1

This is to enforce a good programming practice in MATLAB.

The document you are referred to is located here:
Nested functions: Restrictions on Assigning to Variables

The scoping rules for nested, and in some cases anonymous, functions
require that all variables used within the function be present in the
text of the code. Adding variables to the workspace of this type of
function at run time is not allowed.

MATLAB issues an error if you attempt to dynamically add a variable to
the workspace of an anonymous function, a nested function, or a
function that contains a nested function. …

Loren also has a blog entry about it.

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UPDATE

Have a look on this File Exchange submission:
Pack & Unpack variables to & from structures with enhanced functionality (v2struct).