What is Cognitive Complexity in sonar report?

Cognitive Complexity

After searching some blogs and having chat with sonar team I found an easy definition and calculation of cognitive complexity which is as below:

Definition:

Cognitive Complexity, Because Testability != Understandability

Your written code must be as simple to understand as the above definition, simple.

less Cognitive Complexity more Readability

Let's see a method for example to calculate CC, right now I am referring kotlin language, see below image:

In above image there is a method getAppConfigData(), whose cognitive complexity is being measured. Right now the CC of this method is 18. As you can check in above screen shot there is a warning, which tells that the limit of maximum complexity is 15, which is lower than the current CC of this method.

Now the actual question is: How can I calculate the CC of my method at the time of development?

Follow below rules to get your CC of any method or class as:

• Increment when there is a break in the linear (top-to-bottom, left-to-right) flow of the code
• Increment when structures that break the flow are nested
• Ignore "shorthand" structures that readably condense multiple lines of code into one

So whenever above rules matches, just add + count to your CC and remember count will be increased according to level of code break, as example "if" condition gets +1 if it is the first code break but if you have used one more nested if then it will be a +2 for that inner "if" as shown in below image.

That's all I got in terms of Cognitive Complexity.

You can find everything related to CC at sonar blog

Thank You

More explained answer in Sonar Cognitive Complexity

Basic criteria and methodology A Cognitive Complexity score is assessed according to three basic rules:

1. Ignore structures that allow multiple statements to be readably shorthanded into one
2. Increment (add one) for each break in the linear flow of the code
3. Increment when flow-breaking structures are nested

Additionally, a complexity score is made up of four different types of increments:

• Nesting - assessed for nesting control flow structures inside each other
• Structural - assessed on control flow structures that are subject to a nesting increment, and that increase the nesting count
• Fundamental - assessed on statements not subject to a nesting increment
• Hybrid - assessed on control flow structures that are not subject to a nesting increment, but which do increase the nesting count

While the type of an increment makes no difference in the math - each increment adds one to the final score - making a distinction among the categories of features being counted makes it easier to understand where nesting increments do and do not apply. These rules and the principles behind them are further detailed in the following sections.

In my case the Cognitive Complexity was due to many number of if conditions. My SonarQue allowed only 15 if and else if conditions

if()       =>1
else if()  => 2
.
.
.
else     => 15

Suppose the if exceeds more than 15 conditions it showed me Cognitive Complexity.