How do I call functions with names generated by str2func, varargin, and input argument blocks?

I am building a piece of software which will require the user to write a few short functions of their own. The user will specify a tag and then write a few functions with names that must contain the tag. For example, they could choose tag = "happy" and then would be required to define functions named happy_template.m and happy_plot.m. Then a driver function calls each of these programs as it needs to. The problem is that I would like these user-defined functions to have defaults, and am using argument blocks to do this in my examples. I can't quite figure out how to make this work. Here's a minimal example.

Let the tag be demo_tag. I have created a first file called demo_tag.m.

function demo_tag(opts)

arguments
    opts.x  {mustBeNumeric} = linspace(0,pi);
end

plot(opts.x,sin(opts.x))

I then have a driver function:

function callTagFunction(tag,varargin)

myFunction=str2func(tag);
if nargin ==1
    myFunction();
else
    myFunction(varargin);
end

Then consider the following four calls:

>> demo_tag
>> demo_tag('x',1:10)
>> callTagFunction('demo_tag')
>> callTagFunction('demo_tag','x','1:10')
Error using demo_tag (line 1)
Invalid argument at position 1. A name is expected.

Error in callTagFunction (line 7)
    myFunction(varargin);

The first three work correctly, but the fourth gives errors.

Answer 1

[Stephen23]

function callTagFunction(tag,varargin)
myFunction=str2func(tag);
if nargin ==1
    myFunction();
else
    myFunction(varargin{:});
end %                  ^^^ comma-separated list
end % <- recommended

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html

https://www.mathworks.com/matlabcentral/answers/320713-how-to-operate-on-comma-separated-lists

[Stephen23]

Tested:

demo_tag

demo_tag('x',1:10)

callTagFunction('demo_tag')

callTagFunction('demo_tag','x',1:10) % no problem!

function callTagFunction(tag,varargin)
myFunction=str2func(tag);
if nargin ==1
    myFunction();
else
    myFunction(varargin{:});
end %                  ^^^ comma-separated list
end

function demo_tag(opts)
arguments
    opts.x  {mustBeNumeric} = linspace(0,pi);
end
plot(opts.x,sin(opts.x))
end

[Roy Goodman]

Thanks for the answer and the further references! With your fix, the syntax works even if nargin == 1, so we can simplify the code further to:

function callTagFunction(tag,varargin)
myFunction=str2func(tag);
myFunction(varargin{:});
end

function demo_tag(opts)
arguments
    opts.x  {mustBeNumeric} = linspace(0,pi);
end
plot(opts.x,sin(opts.x))
end

And it even works with the new key/value syntax

>> callTagFunction('demo_tag',x=1:10)