Re: Possible bug in RVO?

[Yuxuan Shui via Digitalmars-d-learn]

On Monday, 4 April 2016 at 03:28:01 UTC, Yuxuan Shui wrote:
I have encountered a weird bug.
I defined a Set class, which has a opBinary!"-". And somehow 
this:

auto tmp = set_a-set_b;

produces different results as this:

set_a = set_a-set_b;

the latter will produce an empty set.

I tried to reduce the source code to get a test case. But this 
problem just goes away after removing some code.

Any ideas what I could have done wrong?

A slightly more reduced test case:

struct Set {
        void insert(ulong v) {
                aa[v] = true;
        }
        @disable this(this);
        bool[ulong] aa;
}
auto clobber(ref Set x, ref Set o) {
        Set ret;
        ret.aa = x.aa;
        return ret;
}
struct XX {
        Set a, b, tmp;
        this(int n) {
                a.insert(1);
		//a.aa[1] = true;  <--- Swap above line with this doesn't 
trigger the bug
                tmp = a.clobber(b);
                a = a.clobber(b);
        }
}
void main(){
        import std.stdio;
        XX xx = XX(0);
        writeln(xx.a.aa.length);
        writeln(xx.tmp.aa.length);
}