Nested redundant 'if' conditions

Question

Is there a better (or cleaner) way to write the following code?

if(conditionX) {     if(condition1)     {         // code X1     }     else if(condition2)     {         // code X2     } } else if(conditionY) {     if(condition1)     {         // code Y1     }     else if(condition2)     {         // code Y2     } } 

I have a few more conditions, but I guess you get the point.

Answer 1

There are four approaches to this problem, none of which is universal:

1. Leave everything as is - There isn't much code duplication here. If computing condition1 and condition2 is tricky, compute them upfront and store them in bool variables
2. Make conditionX and conditionY produce a result that lets you unify condition1 and condition2 - This is not always possible, but in some situations you could prepare a variable that unifies the activities taken in the two branches, say, by using a function pointer or a lambda.
3. Put the processing logic into subclasses with virtual functions to eliminate conditional logic - This is possible only when your initial design missed an opportunity to subclass. Essentially, this approach pushes the decision on conditionX/conditionY into a place where a subclass is created, and then "reuses" that decision later on by calling a proper override of a virtual function in the interface.
4. Create a numeric combination representing all three conditions, and convert to switch - This trick unifies the conditionals, reducing the nesting.

Here is an example of the last approach:

int caseNumber = ((conditionX?1:0) << 3)                | ((conditionY?1:0) << 2)                | ((condition2?1:0) << 1)                | ((condition1?1:0) << 0); switch (caseNumber) {     case 0x09:     case 0x0D:     case 0x0F: // code X1         break;     case 0x0A:     case 0x0E: // code X2         break;     case 0x05:     case 0x07: // code Y1         break;     case 0x06: // code Y2         break; }