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

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 40.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

redundant-parentheses

Control flow constructs (if, else if, switch, for, while, repeat-while, and guard statements), Exception handling constructs (throw, and do/catch statements), and Initializers (array, dictionary, initializer patterns) should not be enclosed in parentheses.

Additionally, method calls with no parameters and a trailing closure should not have empty parentheses following the method name.

Control flow constructs

• if, else if statement

Preferred

if SomeCondition {

} else if SomeOtherCondition {
}

Not Preferred

if (SomeCondition) {

} else if (SomeOtherCondition) {
}

• switch statement

Preferred

switch SomeData {
    default:
        break
}

Not Preferred

switch (SomeData) {
    default:
        break
}

• for loop

Preferred

for var i = 0; i < 10; i+=1 {

}

Not Preferred

for (var i = 0; i < 10; i+=1) {

}

• while loop

Preferred

while SomeCondition {

}

Not Preferred

while (SomeCondition) {

}

• repeat-while loop

Preferred

repeat {

} while SomeCondition

Not Preferred

repeat {

} while (SomeCondition)

• guard clause

Preferred

guard true else {   }

Not Preferred

guard (true) else {   }

Exception handling constructs

• do/catch statement

Preferred

do  {

} catch SomeException {

}

Not Preferred

do  {

} catch (SomeException) {

}

• throw statement

Preferred

throw SomeException

Not Preferred

throw (SomeException)

Initializers

• array items

Preferred

var shoppingList: [String] = ["Eggs", "Milk"]

Not Preferred

var shoppingList: [String] = [("Eggs"), ("Milk")]

• dictionary items

Preferred

var airports: [String: String] = ["YYZ": "Toronto Pearson", "DUB": "Dublin"]

Not Preferred

var airports: [String: String] = [("YYZ"): ("Toronto Pearson"), ("DUB"): ("Dublin")]

• initializer patterns

Preferred

var x: Int = 2
var y: String = "Sleekbyte"
var x = 2

Not Preferred

var x: Int = (2)
var y: String = ("Sleekbyte")
var x = (2)

Method calls

Preferred

items.map {
  item in item.transform()
}

Not Preferred

items.map() {
  item in item.transform()
}