Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

Most of the time a block of code is empty when a piece of code is really missing. So such empty block must be either filled or removed.

Noncompliant Code Example

for ($i = 0; $i < 42; $i++){}  // Empty on purpose or missing piece of code ?

Exceptions

When a block contains a comment, this block is not considered to be empty.

Most of the time a block of code is empty when a piece of code is really missing. So such empty block must be either filled or removed.

Noncompliant Code Example

for ($i = 0; $i < 42; $i++){}  // Empty on purpose or missing piece of code ?

Exceptions

When a block contains a comment, this block is not considered to be empty.

Most of the time a block of code is empty when a piece of code is really missing. So such empty block must be either filled or removed.

Noncompliant Code Example

for ($i = 0; $i < 42; $i++){}  // Empty on purpose or missing piece of code ?

Exceptions

When a block contains a comment, this block is not considered to be empty.

Having two cases in a switch statement or two branches in an if chain with the same implementation is at best duplicate code, and at worst a coding error. If the same logic is truly needed for both instances, then in an if chain they should be combined, or for a switch, one should fall through to the other.

Noncompliant Code Example

switch ($i) {
  case 1:
    doSomething();
    break;
  case 2:
    doSomethingDifferent();
    break;
  case 3:  // Noncompliant; duplicates case 1's implementation
    doSomething();
    break;
  default:
    doTheRest();
}

if ($a >= 0 && $a < 10) {
  doTheThing();
else if ($a >= 10 && $a < 20) {
  doTheOtherThing();
}
else if ($a >= 20 && $a < 50) {
  doTheThing();  // Noncompliant; duplicates first condition
}
else {
  doTheRest();
}

if ($b == 0) {
  doOneMoreThing();
}
else {
  doOneMoreThing(); // Noncompliant; duplicates then-branch
}

var b = a ? 12 > 4 : 4;  // Noncompliant; always results in the same value

Compliant Solution

switch ($i) {
  case 1:
  case 3:
    doSomething();
    break;
  case 2:
    doSomethingDifferent();
    break;
  default:
    doTheRest();
}

if (($a >= 0 && $a < 10) || ($a >= 20 && $a < 50)) {
  doTheThing();
else if ($a >= 10 && $a < 20) {
  doTheOtherThing();
}
else {
  doTheRest();
}

doOneMoreThing();

b = 4;

or

switch ($i) {
  case 1:
    doSomething();
    break;
  case 2:
    doSomethingDifferent();
    break;
  case 3:
    doThirdThing();
    break;
  default:
    doTheRest();
}

if ($a >= 0 && $a < 10) {
  doTheThing();
else if ($a >= 10 && $a < 20) {
  doTheOtherThing();
}
else if ($a >= 20 && $a < 50) {
  doTheThirdThing();
}
else {
  doTheRest();
}

if ($b == 0) {
  doOneMoreThing();
}
else {
  doTheRest();
}

int b = a ? 12 > 4 : 8;

Exceptions

Blocks in an if chain that contain a single line of code are ignored, as are blocks in a switch statement that contain a single line of code with or without a following break.

Having two cases in a switch statement or two branches in an if chain with the same implementation is at best duplicate code, and at worst a coding error. If the same logic is truly needed for both instances, then in an if chain they should be combined, or for a switch, one should fall through to the other.

Noncompliant Code Example

switch ($i) {
  case 1:
    doSomething();
    break;
  case 2:
    doSomethingDifferent();
    break;
  case 3:  // Noncompliant; duplicates case 1's implementation
    doSomething();
    break;
  default:
    doTheRest();
}

if ($a >= 0 && $a < 10) {
  doTheThing();
else if ($a >= 10 && $a < 20) {
  doTheOtherThing();
}
else if ($a >= 20 && $a < 50) {
  doTheThing();  // Noncompliant; duplicates first condition
}
else {
  doTheRest();
}

if ($b == 0) {
  doOneMoreThing();
}
else {
  doOneMoreThing(); // Noncompliant; duplicates then-branch
}

var b = a ? 12 > 4 : 4;  // Noncompliant; always results in the same value

Compliant Solution

switch ($i) {
  case 1:
  case 3:
    doSomething();
    break;
  case 2:
    doSomethingDifferent();
    break;
  default:
    doTheRest();
}

if (($a >= 0 && $a < 10) || ($a >= 20 && $a < 50)) {
  doTheThing();
else if ($a >= 10 && $a < 20) {
  doTheOtherThing();
}
else {
  doTheRest();
}

doOneMoreThing();

b = 4;

or

switch ($i) {
  case 1:
    doSomething();
    break;
  case 2:
    doSomethingDifferent();
    break;
  case 3:
    doThirdThing();
    break;
  default:
    doTheRest();
}

if ($a >= 0 && $a < 10) {
  doTheThing();
else if ($a >= 10 && $a < 20) {
  doTheOtherThing();
}
else if ($a >= 20 && $a < 50) {
  doTheThirdThing();
}
else {
  doTheRest();
}

if ($b == 0) {
  doOneMoreThing();
}
else {
  doTheRest();
}

int b = a ? 12 > 4 : 8;

Exceptions

Blocks in an if chain that contain a single line of code are ignored, as are blocks in a switch statement that contain a single line of code with or without a following break.

Having two cases in a switch statement or two branches in an if chain with the same implementation is at best duplicate code, and at worst a coding error. If the same logic is truly needed for both instances, then in an if chain they should be combined, or for a switch, one should fall through to the other.

Noncompliant Code Example

switch ($i) {
  case 1:
    doSomething();
    break;
  case 2:
    doSomethingDifferent();
    break;
  case 3:  // Noncompliant; duplicates case 1's implementation
    doSomething();
    break;
  default:
    doTheRest();
}

if ($a >= 0 && $a < 10) {
  doTheThing();
else if ($a >= 10 && $a < 20) {
  doTheOtherThing();
}
else if ($a >= 20 && $a < 50) {
  doTheThing();  // Noncompliant; duplicates first condition
}
else {
  doTheRest();
}

if ($b == 0) {
  doOneMoreThing();
}
else {
  doOneMoreThing(); // Noncompliant; duplicates then-branch
}

var b = a ? 12 > 4 : 4;  // Noncompliant; always results in the same value

Compliant Solution

switch ($i) {
  case 1:
  case 3:
    doSomething();
    break;
  case 2:
    doSomethingDifferent();
    break;
  default:
    doTheRest();
}

if (($a >= 0 && $a < 10) || ($a >= 20 && $a < 50)) {
  doTheThing();
else if ($a >= 10 && $a < 20) {
  doTheOtherThing();
}
else {
  doTheRest();
}

doOneMoreThing();

b = 4;

or

switch ($i) {
  case 1:
    doSomething();
    break;
  case 2:
    doSomethingDifferent();
    break;
  case 3:
    doThirdThing();
    break;
  default:
    doTheRest();
}

if ($a >= 0 && $a < 10) {
  doTheThing();
else if ($a >= 10 && $a < 20) {
  doTheOtherThing();
}
else if ($a >= 20 && $a < 50) {
  doTheThirdThing();
}
else {
  doTheRest();
}

if ($b == 0) {
  doOneMoreThing();
}
else {
  doTheRest();
}

int b = a ? 12 > 4 : 8;

Exceptions

Blocks in an if chain that contain a single line of code are ignored, as are blocks in a switch statement that contain a single line of code with or without a following break.

Most of the time a block of code is empty when a piece of code is really missing. So such empty block must be either filled or removed.

Noncompliant Code Example

for ($i = 0; $i < 42; $i++){}  // Empty on purpose or missing piece of code ?

Exceptions

When a block contains a comment, this block is not considered to be empty.

Having two cases in a switch statement or two branches in an if chain with the same implementation is at best duplicate code, and at worst a coding error. If the same logic is truly needed for both instances, then in an if chain they should be combined, or for a switch, one should fall through to the other.

Noncompliant Code Example

switch ($i) {
  case 1:
    doSomething();
    break;
  case 2:
    doSomethingDifferent();
    break;
  case 3:  // Noncompliant; duplicates case 1's implementation
    doSomething();
    break;
  default:
    doTheRest();
}

if ($a >= 0 && $a < 10) {
  doTheThing();
else if ($a >= 10 && $a < 20) {
  doTheOtherThing();
}
else if ($a >= 20 && $a < 50) {
  doTheThing();  // Noncompliant; duplicates first condition
}
else {
  doTheRest();
}

if ($b == 0) {
  doOneMoreThing();
}
else {
  doOneMoreThing(); // Noncompliant; duplicates then-branch
}

var b = a ? 12 > 4 : 4;  // Noncompliant; always results in the same value

Compliant Solution

switch ($i) {
  case 1:
  case 3:
    doSomething();
    break;
  case 2:
    doSomethingDifferent();
    break;
  default:
    doTheRest();
}

if (($a >= 0 && $a < 10) || ($a >= 20 && $a < 50)) {
  doTheThing();
else if ($a >= 10 && $a < 20) {
  doTheOtherThing();
}
else {
  doTheRest();
}

doOneMoreThing();

b = 4;

or

switch ($i) {
  case 1:
    doSomething();
    break;
  case 2:
    doSomethingDifferent();
    break;
  case 3:
    doThirdThing();
    break;
  default:
    doTheRest();
}

if ($a >= 0 && $a < 10) {
  doTheThing();
else if ($a >= 10 && $a < 20) {
  doTheOtherThing();
}
else if ($a >= 20 && $a < 50) {
  doTheThirdThing();
}
else {
  doTheRest();
}

if ($b == 0) {
  doOneMoreThing();
}
else {
  doTheRest();
}

int b = a ? 12 > 4 : 8;

Exceptions

Blocks in an if chain that contain a single line of code are ignored, as are blocks in a switch statement that contain a single line of code with or without a following break.

Most of the time a block of code is empty when a piece of code is really missing. So such empty block must be either filled or removed.

Noncompliant Code Example

for ($i = 0; $i < 42; $i++){}  // Empty on purpose or missing piece of code ?

Exceptions

When a block contains a comment, this block is not considered to be empty.