The IF/ELSE Deadly Spiral

else if ($e) { //...
}
}
else { //...
}
}
}

It did happen to you too, didn’t it?

Of course, it's better to avoid such complex IF/ELSE blocks.
For three reasons:

They make your code really hard to understand.
Changing the IF/ELSE logic, or adding a new condition, becomes too difficult and error-prone.
With too many different cases, you are likely going to duplicate some code.

So, let’s see 3 techniques to avoid the IF/ELSE deadly spirals in the first place.

1. Use multiple return exit points.

This is the easiest technique to use in functions and class methods, where the different IF/ELSE cases select the value to be returned.
The idea is to return the value immediately after each condition, so that the next conditions are automatically excluded.

For example:

if ($firstCondition) {
return $firstValue;
}
if ($secondCondition) {
return $secondValue;
}
return $thirdValue;

This solution helps avoiding IF/ELSE nesting in those cases where each condition excludes the others.
By returning the value right away, the next code block is only executed if the first condition is false.

I don’t really like this solution, though.
If you remember my "clean code" tips, you know that I prefer to have a single, final return point.
Moreover, with multiple return statements it is hard to understand what value the function returns.

Which brings us to the second solution.

2. Use a NULL-initialized value.

Here it is a better implementation of the previous solution.
First, you initialize the return value to NULL.
Then, instead of nesting multiple IF/ELSE conditions, you use the return value as a sentinel.

For example:

$return = NULL;
if ($firstCondition) {
$return = $firstValue;
}
if (is_null($return) && $secondCondition) {
$return = $secondValue;
}
if (is_null($return) && $thirdCondition) {
$return = $thirdValue;
}
return $return;

The advantages over the previous solution is that you have only a single, final return point. On top of that, this solution works if you are not inside a function or class method.

3. Refactor your code into functions.

Finally, let's see a more radical approach.
Depending on the specific logic of your IF/ELSE blocks, you can implement the condition checks into functions.
Then, you can replace the IF/ELSE tree with calls to these functions. Each function will perform a condition check and return the proper value.

For example:
$value = funct1($cond1, $cond2);
$value = funct2($value, $cond3);
$value = funct3($value, $cond4);

Each function can take the current $value as well as one or more additional conditions ($cond1, $cond2, $cond3...) as arguments and return a new value.
You can also group the whole procedure into a single function containing all the above function calls.

Here is a concrete example.
Let's say that you want to know how many days a year has.
To check whether a year is a leap year, you need to check that it is divisible by 4, but not by 100 unless it is also divisible by 400.

Instead of using IF/ELSE conditions, you can perform the following function calls:

$divBy4 = divisibleBy4($year);
$divBy100 = divisibleBy100($year);
$divBy400 = divisibleBy400($year);
$isLeap = isLeapYear($divBy4, $divBy100, $divBy400);

The isLeapYear() function returns true if $divBy4 is true and either $divBy400 is true or $divBy100 is false.
You don't need any IF at all in all those functions.
Even the last check is easy enough to be done in a single line:
return $divBy4 && (!$divBy100 || $divBy400);

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