Dynamically assign function to object method

I am trying to design an optimization object, where I can dynamically change the costfunction to minimize.

What I need is a good way to implement this behaviour in Matlab.

Here is my minimal working example, with what my testcase should be able to do:

clc, clear all, close all

obj = SetMethodClass();
obj.methodToEvaluate = 'cube';
twentyseven = obj.evalFcn(3)

obj.methodToEvaluate = 'square';
nine = obj.evalFcn(3)

Here is what my class implementation looks like:

    classdef SetMethodClass < matlab.mixin.SetGet
        properties
            methodToEvaluate@char
        end
        properties (SetAccess = protected)
            handleToEvaluationFcn@function_handle
        end

        methods
            function set.methodToEvaluate(obj, method)
                if ismember(method,{'square', 'cube'})
                    obj.methodToEvaluate = method;

                    %doesn't work (of course ;))
    %                 obj.handleToEvaluationFcn = obj.(method);

                    %doesn't work
    %                 obj.handleToEvaluationFcn = @obj.(method);

                    %doesn't work either ;)
    %                 obj.handleToEvaluationFcn = str2func(['obj.' method]);

                    %now this does work, but it's ugly and I don't like switch case
                    switch lower(obj.methodToEvaluate)
                        case 'square', obj.handleToEvaluationFcn = @obj.square; %#ok
                        case 'cube', obj.handleToEvaluationFcn = @obj.cube; %#ok
                        otherwise, error('This method does not exist');
                    end                
                else
                    error([class(obj) ': %s is not a function to Evaluate'], method);
                end
            end
            function y = evalFcn(obj,x)
                y = obj.handleToEvaluationFcn(x);
            end
        end
        methods(Access = private)
            function y = square(~,x)
                y = x^2;
            end
            function y = cube(~,x)
                y = x^3;
            end
        end
    end