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

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

forced-type-cast

Avoid using the forced form of the type cast operator (as!) because Swift is not able to determine at compile time if the type conversion will succeed. In the event of an unsuccessful conversion, a runtime error will be triggered. The conditional form of the type cast operator (as?) is safer and should be used when possible.

Preferred

if let movie = item as? Movie {
    print("Movie: '\(movie.name)', dir. \(movie.director)")
}

Not Preferred

let movie = item as! Movie
print("Movie: '\(movie.name)', dir. \(movie.director)")

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 240.

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

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 52.

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

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 52.

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

comment-whitespace

Prefer at least one whitespace character after a comment opening symbol (//, ///, /*, or /**) and at least one whitespace character before a comment closing symbol (*/).

Preferred

// This is a comment

/// This is a documentation comment

/* This is a
multi-line comment */

/* This is a
multi-line comment
*/

/** This is a
documentation multi-line
comment
*/

Not Preferred

//This is a comment

///This is a documentation comment

/*This is a
multi-line comment*/

/**This is a multi-line
documentation comment */

terminating-semicolon

Swift does not require a semicolon after each statement in your code unless you wish to combine multiple statements on a single line. Do not write multiple statements on a single line separated with semicolons.

Imports

Preferred

import Foundation

Not Preferred

import Foundation;

Enums and enum cases

Preferred

enum CompassPoint {
    case North
    case South
    case East
    case West
}

Not Preferred

enum CompassPoint {
    case North;
    case South;
    case East;
    case West;
};

Protocols

Preferred

protocol SomeProtocol {
    var SomeMethod: String { get }
    func SomeMethod()
    func SomeMethod(f: Int)
    func SomeMethod(bar: String, baz: Double)
}

Not Preferred

protocol SomeProtocol {
    var SomeMethod: String { get };
    func SomeMethod();
    func SomeMethod(f: Int);
    func SomeMethod(bar: String, baz: Double);
};

Extensions

Preferred

extension SomeType {

}

Not Preferred

extension SomeType {

};

Structs

Preferred

struct DemoStruct {
        var x: String // variables
}

Not Preferred

struct DemoStruct {
        var x: String // variables
};

Classes

Preferred

class SomeClass {
    let b = 2 // constants
}

Not Preferred

class SomeClass {
    let b = 2 // constants
};

Loops

Preferred

// while loop
while true {

}

// for loop
for ; ; {
}

// repeat while
repeat {

} while true

Not Preferred

// while loop
while true {

};

// for loop
for ; ; {
};

// repeat while
repeat {

} while true;

todo-syntax

TODO comments should be defined separately using non-nested single line comments. They should adhere to the <TODO: description> or <TODO(developer-name): description> syntax. Empty TODO comments will be flagged.

Preferred

// TODO: <insert mandatory todo comment>
// TODO(dev-name): <insert mandatory todo comment></insert></insert>

Not Preferred

// TODO:

/// TODO: Documentation comments should not have TODOs

//// TODO: Nested comments should not have TODOs

// //TODO: Nested comments should not have TODOs

// TODO: Nested comments should not have TODOs // some comment

//// TODO: Nested comments should not have TODOs

function-whitespace

Every function and method declaration should have one blank line before and after itself. An exception to this rule are functions that are declared at the start of a file (only need one blank line after their declaration) or at the end of a file (only need one blank line before their declaration). Comments immediately before a function declaration (no blank lines between them and the function) are considered to be part of the declaration.

Preferred

func function1() {
  var text = 1
  var text = 2
}

function1()

// a comment
func function2() {
  // something goes here
}

struct SomeStruct {

  func function3() {
    // something goes here
  }

  func function4() {
    // something else goes here
  };

}

func function5() {
  // something goes here
}

Not Preferred

func function1() {
  var text = 1
  var text = 2
}
function1()
// a comment
func function2() {
  // something goes here
}

struct SomeStruct {
  func function3() {
    // something goes here
  }

  func function4() {
    // something else goes here
  };
}
func function5() {
  // something goes here
}