Comma operator overloading

[Jay Norwood]

I'm reading a SystemC lecture which describes use of operator 
overloading of comma in their syntax to support concatenation.

So, for example, they support the data operations below
sc_uint<4> a, b, d, e;
sc_unit<8> c;
c = (a, b);
(d, e) = c;

As I understand it, SystemC is C++.

I didn't find commas among the overloadable D operators.   Is 
that correct?