MATLAB `builtin` calls overloaded function

Question

% Dog.m -------------------------------------------------
classdef Dog
    methods
        function varargout = subsref(obj, x)
            varargout = subsref_overloaded(obj, x);
        end
    end
end

% subsref_overloaded.m ----------------------------------
function varargout = subsref_overloaded(obj, x)
    [varargout{1:nargout}] = builtin('subsref', obj, x);
end

d=Dog() , and d() yields

Maximum recursion limit of 500 reached.

Error in Dog (line 2)
    [varargout{1:nargout}] = builtin('subsref', obj, x);

Caused by:
    Maximum recursion limit of 500 reached.

Why, and can it be fixed? It's strange since it copies code straight from implementation , and in debugger, builtin('subsref', obj, x) called while in Dog.m works as expected, but not while in subsref_overloaded.m .

---

Context : I'm overloading subsref like here , but that's verbose to reuse so I want to make something like subsref_overloaded(obj, x, fn) and output fn(x) .

Answer 1

builtin cares about where it's called from for some reason - it works properly if called from within the class itself (thanks @CrissLuengo). The following is an imperfect workaround

classdef Dog
    methods
        function varargout = subsref(obj, x)
            [varargout{1:nargout}] = subsref_overloaded(obj, x);
            if ~isempty(varargout) && varargout{1} == "special token"
                [varargout{1:nargout}] = builtin('subsref', obj, x);
            end
        end
    end
end

function varargout = subsref_overloaded(obj, x)
    if % your cond here
        % your logic here
    else
        [varargout{1:nargout}] = "special token";
    end
end

Better alternatives / explanations welcome.