Is it acceptable to only use the 'else' portion of an 'if-else' statement?

Question

Sometimes, I feel like it is easier to check if all of the conditions are true, but then only handle the "other" situation.

I guess I sometimes feel that it is easier to know that something is valid, and assume all other cases are not valid.

For example, let's say that we only really care about when there is something wrong:

object value = GetValueFromSomeAPIOrOtherMethod();  if((value != null) && (!string.IsNullOrEmpty(value.Prop)) && (possibleValues.Contains(value.prop))) {     // All the conditions passed, but we don't actually do anything } else {     // Do my stuff here, like error handling } 

Or should I just change that to be:

object value = GetValueFromSomeAPIOrOtherMethod();  if((value == null) || (string.IsNullOrEmpty(value.Prop)) || (!possibleValues.Contains(value.prop))) {     // Do my stuff here, like error handling } 

Or (which I find ugly):

object value = GetValueFromSomeAPIOrOtherMethod();  if(!((value != null) && (!string.IsNullOrEmpty(value.Prop)) && (possibleValues.Contains(value.prop)))) {     // Do my stuff here, like error handling } 

Answer 1

Though rare for me, I sometimes feel that writing in this form leads to the clearest code in some cases. Go for the form that provides the most clarity. The compiler won't care, and should generate essentially (probably exactly) the same code.

It may be clearer, though, to define a boolean variable that is assigned the condition in the if () statement, then write your code as a negation of that variable:

bool myCondition = (....); if (!myCondition) {     ... } 

Answer 2

Having an empty if block with statements in the else is ... just bad style. Sorry, this is one of my pet peeves. There is nothing functionally wrong with it, it just makes my eyes bleed.

Simply ! out the if statement and put your code there. IMHO it reduces the noise and makes the code more readable.