Warn about do nothing expressions?

[Benjamin Thaut]

Am 28.03.2014 18:03, schrieb monarch_dodra:
> On Friday, 28 March 2014 at 16:54:49 UTC, Benjamin Thaut wrote:
>> I had a bug which came down to the following line today:
>>
>> m_takeIndex = m_takeIndex++;
>>
>> Actually this line does nothing. m_takeIndex remains at exactly the
>> same value as before (tested with dmd 2.065).
>>
>> Can someone please explain why?
>
> IT does nothing because that's post-increment: EG "save the current
> value, increment, return the old value".
>
> Then you assign back the old value, effectively putting you back where
> you started:
>
> int i = 5;
>
> i = i++; //i is 5
> then
> i = 5; //i was incremented to 6
> then
> i is 5 again;
>
>> And would be suitable to warn about this, if it is correct behaviour?
>
> The problem here though is that we are talking about a "logical" no side
> effect: It *does* something, you just can't observe it.
>
> Imagine this:
>
> //----
> void fun(ref i, ref j)
> {
>      i = j++;
> }
> void main()
> {
>      int a = 5;
>      fun(a, a); //do nothing?
> }
> //----
>
> This is to contrast with "i + j;" which is an *actual* no op.

Well when I mean warning, I really only mean the

var = var++

case without any indirections. Because I can't think of a case where you 
actually want this.

Kind Regards
Benjamin Thaut