Methods of simplifying ugly nested if-else trees in C#

Question

Sometimes I\'m writing ugly if-else statements in C# 3.5; I\'m aware of some different approaches to simplifying that with table-driven development, class hierarchy, anonimous m

Answer 1

One thing I find myself doing at times is inverting the condition followed by return; several such tests in a row can help reduce nesting of if and else.

Answer 2

Good question. "Conditional Complexity" is a code smell. Polymorphism is your friend.

Conditional logic is innocent in its infancy, when it’s simple to understand and contained within a few lines of code. Unfortunately, it rarely ages well. You implement several new features and suddenly your conditional logic becomes complicated and expansive. [Joshua Kerevsky: Refactoring to Patterns]

One of the simplest things you can do to avoid nested if blocks is to learn to use Guard Clauses.

double getPayAmount() {
if (_isDead) return deadAmount();
if (_isSeparated) return separatedAmount();
if (_isRetired) return retiredAmount();
return normalPayAmount();
};  

The other thing I have found simplifies things pretty well, and which makes your code self-documenting, is Consolidating conditionals.

double disabilityAmount() {
    if (isNotEligableForDisability()) return 0;
    // compute the disability amount

Other valuable refactoring techniques associated with conditional expressions include Decompose Conditional, Replace Conditional with Visitor, Specification Pattern, and Reverse Conditional.

Answer 3

I know that this is not the answer you are looking for, but without context your questions is very hard to answer. The problem is that the way to refactor such a thing really depends on your code, what it is doing, and what you are trying to accomplish. If you had said that you were checking the type of an object in these conditionals we could throw out an answer like 'use polymorphism', but sometimes you actually do just need some if statements, and sometimes those statements can be refactored into something more simple. Without a code sample it is hard to say which category you are in.

Answer 4

Not a C# answer, but you probably would like pattern matching. With pattern matching, you can take several inputs, and do simultaneous matches on all of them. For example (F#):

let x=
  match cond1, cond2, name with
  | _, _, "Bob"     -> 9000 // Bob gets 9000, regardless of cond1 or 2
  | false, false, _ -> 0 
  | true, false, _  -> 1
  | false, true, _  -> 2
  | true, true, ""  -> 0 // Both conds but no name gets 0
  | true, true, _   -> 3 // Cond1&2 give 3

You can express any combination to create a match (this just scratches the surface). However, C# doesn't support this, and I doubt it will any time soon. Meanwhile, there are some attempts to try this in C#, such as here: http://codebetter.com/blogs/matthew.podwysocki/archive/2008/09/16/functional-c-pattern-matching.aspx. Google can turn up many more; perhaps one will suit you.

Answer 5

I was told years ago by an instructor that 3 is a magic number. And as he applied it it-else statements he suggested that if I needed more that 3 if's then I should probably use a case statement instead.

   switch (testValue)
   {
      case = 1:
         // do something
         break;
      case = 2:
         // do something else
         break;
      case = 3:
         // do something more
         break;
      case = 4
         // do what?
         break;
      default:
         throw new Exception("I didn't do anything");
   }

If you're nesting if statements more than 3 deep then you should probably take that as a sign that there is a better way. Probably like Avirdlg suggested, separating the nested if statements into 1 or more methods. If you feel you are absolutely stuck with multiple if-else statements then I would wrap all the if-else statements into a single method so it didn't ugly up other code.