Learning Functional Programming in Go

After applying Replace Parameter with Method technique

After refactoring our code per our instructions, we have removed a parameter. Now we only have one parameter:

 lineItemPrice := quantity * itemPrice; totalPrice := getDiscountedPrice(lineItemPrice);

How will code maintainers know that the totalPrice can be reduced by a discount?

Does hiding the discount parameter improve understandability or does it actually increase code complexity?