I often encounter code like this:

if (rowCount > rowIdx) { if (drc[rowIdx].Table.Columns.Contains("avalId")) { do { if (Attributes[attrVal.AttributeClassId] == null) { // do stuff } else { if (!(Attributes[attrVal.AttributeClassId] is ArrayList)) { // do stuff } else { if (!isChecking) { // do stuff } else { // do stuff } } } rowIdx++; } while (rowIdx < rowCount && GetIdAsInt32(drc[rowIdx]) == Id); } else rowIdx++; } return rowIdx; }

The excessive nesting of conditional clauses pushes the code out into an arrow formation:

if if if if do something endif endif endif endif

And you know you're definitely in trouble when the code you're reading is regularly exceeding the right margin on a typical 1280x1024 display. This is the Arrow Anti-Pattern in action.

One of my primary refactoring tasks is "flattening" arrow code like this. Those sharp, pointy barbs are dangerous! Arrow code has a high cyclomatic complexity value – a measure of how many distinct paths there are through code:

Studies show a correlation between a program's cyclomatic complexity and its error frequency. A low cyclomatic complexity contributes to a program's understandability and indicates it is amenable to modification at lower risk than a more complex program. A module's cyclomatic complexity is also a strong indicator of its testability.

Where appropriate, I flatten that arrow code by doing the following:

Replace conditions with guard clauses. This code.. if (SomeNecessaryCondition) { // function body code } .. works better as a guard clause: if (!SomeNecessaryCondition) { throw new RequiredConditionMissingException; } // function body code Decompose conditional blocks into seperate functions. In the above example, we're in a do..while loop which could be decomposed: do { ValidateRowAttribute(drc[rowIdx]); rowIdx++; } while(rowIdx < rowCount && GetIdAsInt32(drc[rowIdx]) == Id); Convert negative checks into positive checks. As a broad rule, I prefer to put the positive comparison first and let the negative comparison fall out naturally into the else clause. I think this reads a lot better and, more importantly, avoids the "I ain't not never doing that" syndrome: if (Attributes[attrVal.AttributeClassId] is ArrayList) { // do stuff } else { // do stuff } Always opportunistically return as soon as possible from the function. Once your work is done, get the heck out of there! This isn't always possible – you might have resources you need to clean up. But whatever you do, you have to abandon the ill-conceived idea that there should only be one exit point at the bottom of the function.

The goal is to have code that scrolls vertically a lot… but not so much horizontally.