Matlab: Improper index matrix reference (or outsmarting matlab)

Question

I want to be able to write jasmine-like tests in Matlab. So something like

expect(myfibonacci(0)).toBe(0);
expect(myfibonacci(5)).toBe(15);
expect(myfibonacci(10         


        

Answer 1

To add to @MohsenNosratinia's remark, if you use nested-functions/closure instead of OOP classes, you get the yet another inconsistency:

function obj = expect(expr)
    obj = struct();
    obj.toBe = @toBe;
    function toBe(expected)
        assert(isequal(expr,expected))
    end
end

1. The syntax doesn't work from the command prompt:

   >> expect(1+1).toBe(2)
   Undefined variable "expect" or class "expect". 
   

2. Doesn't work either from a script:

   testScript.m

   expect(1+1).toBe(2)
   expect(1*1).toBe(2)
   

   with the same error as before:

   >> testScript
   Undefined variable "expect" or class "expect".
   Error in testScript (line 1)
   expect(1+1).toBe(2)
   

3. But for an M-file function:

   testFcn.m

   function testFcn
       expect(1+1).toBe(2)
       expect(1*1).toBe(2)
   end
   

   it is strangely accepted:

   >> testFcn
   Error using expect/toBe (line 5)
   Assertion failed.
   Error in testFcn (line 3)
       expect(1*1).toBe(2) 
   

   (the second assertion failed as expected, but no syntax errors!)

---

I consider throwing a "syntax error" to be the correct outcome here, as you should not directly index into the result of a function call. If you do, I think of it as "undefined behavior" :) (it might work, but not in all cases!)

Instead, you should first store the result in a temporary variable, then apply indexing into it:

>> obj = expect(1+1);
>> obj.toBe(2);

or resort to ugly hacks like:

>> feval(subsref(expect(1+1), substruct('.','toBe')), 2)

or even undocumented functions:

>> builtin('_paren', builtin('_dot', expect(1+1), 'toBe'), 2)