Does D automatically rewrite opBinary to opOpAssign?

Question

for example, assuming that T implements the right operator overloads:

T t1, t2, t3;
t3 = t1 + t2; // t3.opAssign(t1.opBinary!"+"(t2)) for sure
t3 = t3 + t2; // rewritten to t3.opOpAssign!"+"(t2) ?

Is the last operation optimized by D ?

Answer 1

No, it is not. It is not possible, because opBinary and opOpAssign could have different semantic:

struct S
{
    int val = 5;

    S opBinary(string op)(S rhs) if (op == "+")
    {
        return S(val + rhs.val);
    }

    void opOpAssign(string op)(S rhs) if (op == "+")
    {
        val = val - rhs.val;
    }
}

void main()
{
    import std.stdio;

    S s1, s2, s3;
    writeln(s3); // S(5)

    s3 = s3 + s2;
    writeln(s3); // S(10)

    s3.val = 5;
    writeln(s3); // S(5)

    s3 += s2;
    writeln(s3); // S(0)
}