Question

Recently I’ve been working on legacy vb.net code and during code peer review it was recommended not to use Exit Sub / Function but instead to nest all functionality in IF statements.

When I initially started developing I used to do it this way instinctively (Nest the IF’s), not only did it seem more logical, it just seemed less confusing.

However at some point I worked with a team that treated nested IF’s as “evil”, and so Exit subs / functions I was told was preferred. I’m pretty sure they produced some MS best practice material to back this up.

So this question is for experienced developers, which way is truly preferred? If you give an answer could you also please state your sources, or just mention that this is a preference preferred by your team / company / personal and give reasons.

Thanks in advance.

EDIT as requested: Code Samples

Exit Sub :

Private Sub DoSomeWork()
 if not conditionMetFromAnotherFunction() then
      exit Sub 
 end if

 'Method work starts here
End Sub

Nested IFs:

Private Sub DoSomeWork()
 if conditionMetFromAnotherFunction() then
     'Method work starts here
 end if
End Sub

Answer 1

As David pointed out in his comment, nested if statements can add to the complexity of your code.

Imagine the following (simplified) code :

Private Sub DoSomeWork()
    if conditionMetFromAnotherFunction() then
        if conditionDependantUponPreviousCondition then
            ' Do the work
        end if
    end if
End Sub

Or the following

Private Sub DoSomeWork()
    if not conditionMetFromAnotherFunction()
        return
    else if not conditionDependantUponPreviousCondition 
        return
    end if


    ' If we're here, everything's all good
    ' Do the work...
End Sub

If your conditions get more complex, returning makes it much more easy to understand that under some conditions, your code is not doing anything, and makes your code more readable.

Otherwise, you have to read all the function and mentally parse the nested if’s to see that nothing’s done.