System.Linq.Expressions.Expression.MakeOpAssignUnary C# (CSharp) Method

        private static UnaryExpression MakeOpAssignUnary(ExpressionType kind, Expression expression, MethodInfo method)
        {
            RequiresCanRead(expression, nameof(expression));
            RequiresCanWrite(expression, nameof(expression));

            UnaryExpression result;
            if (method == null)
            {
                if (expression.Type.IsArithmetic())
                {
                    return new UnaryExpression(kind, expression, expression.Type, null);
                }
                string name;
                if (kind == ExpressionType.PreIncrementAssign || kind == ExpressionType.PostIncrementAssign)
                {
                    name = "op_Increment";
                }
                else
                {
                    Debug.Assert(kind == ExpressionType.PreDecrementAssign || kind == ExpressionType.PostDecrementAssign);
                    name = "op_Decrement";
                }
                result = GetUserDefinedUnaryOperatorOrThrow(kind, name, expression);
            }
            else
            {
                result = GetMethodBasedUnaryOperator(kind, expression, method);
            }
            // return type must be assignable back to the operand type
            if (!TypeUtils.AreReferenceAssignable(expression.Type, result.Type))
            {
                throw Error.UserDefinedOpMustHaveValidReturnType(kind, method.Name);
            }
            return result;
        }
    }