ref + operator overloading question

[Namespace]

On Monday, 16 September 2013 at 21:01:48 UTC, Aleksey wrote:
> On Monday, 16 September 2013 at 20:53:18 UTC, Namespace wrote:
>> On Monday, 16 September 2013 at 20:43:01 UTC, Aleksey wrote:
>>> I get strange type errors in the following code, and I don't
>>> understand why =( Could anybody help?
>>>
>>> struct I {
>>>     int i;
>>>     I opBinary(string op)(ref I that)
>>>     if (op == "+") {
>>>         return I(i + that.i);
>>>     }
>>> }
>>>
>>> void main() {
>>>     auto a = I(1);
>>>     auto d = a + (a + a);
>>> }
>>>
>>> Error: incompatible types for ((a) + (a.opBinary(a))): 'I' 
>>> and 'I'
>>>
>>> If I remove ref or parens around (a+a) the code compiles just
>>> fine.
>>
>> opBinary returns a rvalue. But your code accepts only lvalues.
>> (a + a) produce an rvalue so a + (a + a) is the same as lvalue 
>> + rvalue and rvalues aren't accepted. You could use auto ref 
>> for that purpose.
>
> Thank you! auto ref is exactly what I was looking for!

You should know, that auto ref is only useable for template 
functions/methods. Maybe this will change, but not in the next 
years.