How do I overload += operator?

[Adam D. Ruppe]

On Monday, 25 January 2021 at 17:09:22 UTC, Jack wrote:
>     auto ref opAssign(string op, T)(T value)

try

opOpAssign instead

opAssign is for =

opOpAssign is for +=, -=, etc.

It might be some variation but I think it works if you just 
rename it.