function setdefaults(defaults)
    var_names = evalin('caller', 'who');
    default_names = fieldnames(defaults);
    must_replace = ~ismember(default_names, var_names);
    for k = find(must_replace)'
        name = default_names{k};
        assignin('caller', name, defaults.(name));
    end
end

I’ve been testing it and it’s pretty handy.

The first method is great, however I’m a bit turned off by the fact that the inputs are all lumped into varargin. As I grew accustomed to Matlab, I learned to identify a function’s arguments with a quick glance at the top line.

I was thinking of accepting the inputs as usual, define a struct with the default values, and pass it to a helper function. The helper function accesses the main function’s variables as defined in the struct, and writes the default values if needed. IMHO it could be an excellent compromise :)

function testing()
    something('testing ', 'it')
    something()
end

function z = something(a, b, c)
    defaults.a = 'hey ';
    defaults.b = 'you';
    defaults.c = '!';
    setdefaults(defaults);

    z = [a b c];
end

function setdefaults(defaults)
    var_names = evalin('caller', 'whos');
    default_names = fieldnames(defaults);
    must_replace = ~ismember(default_names, var_names);
    for k = find(must_replace)
        name = default_names(k);
        assignin('caller', name, defaults.(name));
    end
end

Unfortunately I don’t know of a way to do that right now. Having syntax-highlighted code is on our wish list too.

–Loren

I just posted the feature request as suggested.

I realized that I did not provide the way I currently consider the most suitable for me. I have converged to an approach very similar to the one in Ben’s comments of the previous article, i.e. using key-value pairs, with defaults defined in a structure in the beginning of a function and then overwriting them with the respective fields of parameters structure.

The only difference is that I prefer to allow for key-value pairs given in the same way as in many MATLAB graphics commands (i.e. converting the varargin cell array to structure inside the function), rather then directly expecting a structure as an argument.

Thanks for showing all these possibilities.

I believe R does something similar as well. Can you please put this into our system as an enhancement request here? It would be more meaningful coming directly from a customer. Thanks.

–Loren

I have been trying to find the optimal way of dealing with optional arguments and default values for several years, but I find myself of not being able to stick with one best approach. I am trying new ways over and over.

I must actually say, that I like the Python way of dealing with optional arguments and default values, i.e. specifying them directly in the function header. It would be nice to have this feature in MATLAB as well:

function foo(reqArg, optArg1=12, optArg2=’whatever’)

Petr

I could definitely use nargchk but mentally what I am doing is simple enough that I don’t think to. It doesn’t help with setting the defaults either.

–Loren