How do I overload += operator?

[Q. Schroll]

On Monday, 25 January 2021 at 21:53:15 UTC, Jack wrote:
> That naming is confusing

op: it is an operator method
Op: it takes an operator as a parameter
Assign: kinda obvious.

As an example, there are opIndex, opIndexAssign and 
opIndexOpAssign.
opIndex overloads obj[i].
opIndexAssign overloads obj[i] = rhs, and
opIndexOpAssign overloads opj[i] += rhs.

Maybe, in the greater scheme, the naming makes more sense to you.