BigInt.opOpAssign
BigInt opOpAssign(string op, T)(T y) if ((op == "+" || op == "-" || op == "*" || op == "/" || op == "%"
|| op == ">>" || op == "<<" || op == "^^" || op == "|" || op == "&" || op == "^") && isIntegral!T) pure nothrow @safe return scopeImplements assignment operators from built-in integers of the form BigInt op= integer.