#pragma mark in Swift?

Question

In Objective C, I can use #pragma mark to mark sections of my code in the symbol navigator. Since this is a C preprocessor command, it's not available in Swift. Is there a stand-in for this in Swift, or do I have to use ugly comments?

Answer 1

You can use // MARK:

---

There has also been discussion that liberal use of class extensions might be a better practice anyway. Since extensions can implement protocols, you can e.g. put all of your table view delegate methods in an extension and group your code at a more semantic level than #pragma mark is capable of.

Answer 2

Up to Xcode 5 the preprocessor directive #pragma mark existed.

From Xcode 6 on, you have to use // MARK:

These preprocessor features allow to bring some structure to the function drop down box of the source code editor.

some examples :

// MARK:

-> will be preceded by a horizontal divider

// MARK: your text goes here

-> puts 'your text goes here' in bold in the drop down list

// MARK: - your text goes here

-> puts 'your text goes here' in bold in the drop down list, preceded by a horizontal divider

update : added screenshot 'cause some people still seem to have issues with this :

Answer 3

For those who are interested in using extensions vs pragma marks (as mentioned in the first comment), here is how to implement it from a Swift Engineer:

import UIKit

class SwiftTableViewController: UITableViewController {

    init(coder aDecoder: NSCoder!) {
        super.init(coder: aDecoder)

    }

    override func viewDidLoad() {
        super.viewDidLoad()

    }
}

extension SwiftTableViewController {
    override func numberOfSectionsInTableView(tableView: UITableView?) -> Int {
        return 1
    }

    override func tableView(tableView: UITableView?, numberOfRowsInSection section: Int) -> Int {
        return 5
    }

    override func tableView(tableView: UITableView?, cellForRowAtIndexPath indexPath: NSIndexPath?) -> UITableViewCell? {
        let cell = tableView?.dequeueReusableCellWithIdentifier("myCell", forIndexPath: indexPath) as UITableViewCell;

        cell.textLabel.text = "Hello World"

        return cell
    }

}

It's also not necessarily the best practice, but this is how you do it if you like.

Answer 4

Pragma mark - [SOME TEXT HERE] was used in Objective-C to group several function together by line separating.

In Swift you can achieve this using MARK, TODO OR FIXME

i. MARK : //MARK: viewDidLoad

This will create a horizontal line with functions grouped under viewDidLoad(shown in screenshot 1)

ii. TODO : //TODO: - viewDidLoad

This will group function under TODO: - viewDidLoad category (shown in screenshot 2)

iii. FIXME : //FIXME - viewDidLoad

This will group function under FIXME: - viewDidLoad category (shown in screenshot 3)

Check this apple documentation for details.

Answer 5

Official Documentation

Apple's official document about Xcode Jump Bar: Add code annotations to the jump bar

Jump Bar Screenshots for Sample Code

Behavior in Xcode 10.1 and macOS 10.14.3 (Mojave)

Behavior in Xcode 10.0 and macOS 10.13.4 (High Sierra)

Behavior in Xcode 9.4.1 and macOS 10.13.0

Discussion

!!!: and ???: sometimes are not able to be displayed.

Answer 6

In Objective-C code Xcode detects comments like // MARK: - foo which is a bit more portable than #pragma. But these do not seem to be picked up, too (yet?).

Edit: Fixed in Xcode 6 beta 4.

Answer 7

Xcode 8 now handles it as followed and shows up like this in the method dropdown:

Answer 8

I think Extensions is a better way instead of #pragma mark.

The Code before using Extensions:

class ViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate {
    ...

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        ...
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        ...
    }

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        ...
    }
}

The code after using Extensions:

class ViewController: UIViewController {
    ...
}

extension ViewController: UICollectionViewDataSource {
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        ...
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        ...
    }
}

extension ViewController: UICollectionViewDelegate {
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
       ...
    }
}

Answer 9

Confirmed with an Apple Engineer in the Swift lab this morning at WWDC that there currently aren't any #pragma or equivalent at the moment, they consider this a bug, and it will arrive soon, so I am guessing beta 2, I hope.

Anyway, it's on it's way.

---

Xcode now supports //MARK:, //TODO: and //FIXME landmarks to annotate your code and lists them in the jump bar

Answer 10

There are Three options to add #pragma_mark in Swift:

1) // MARK: - your text here -

2) // TODO: - your text here -

3) // FIXME: - your text here -

Note: Uses - for add separators

Answer 11

Use

// MARK: SectionName

or

// MARK: - SectionName

This will give a line above pragma mark, making it more readable.

For ease just add

// MARK: - <#label#>

to your code snippets.

Alternate way -

Use it in this way

private typealias SectionName = ViewController
private extension SectionName  {
    // Your methods
}

This will not only add mark(just like pragma mark) but also segregate the code nicely.

Answer 12

//# MARK: - Spinner Class Methods

Add a line between the colon and your description to insert a separator line. This helps to organize your code even more. The code and screenshot above make use of the MARK comment with a line included.

1. //# MARK: – Text Methods (LINE)
2. //# MARK: Text Methods (NO LINE)

This only works with the MARK comment.

Answer 13

You may also be interested in Swift 4.2 / XCode 10 compiler directives like

#warning("Some string to display")

and

#error("Some error to display")

It might be useful when you really don't want to miss something.

Answer 14

Professional programer must be use this tag for good code. It is also good for team work.

// MARK: example Web Service start here
// TODO: example 1
// FIXME: Please change BASE url before live 

It is easy to find method like this

Answer 15

In Xcode 11 they added minimap which can be activated Editor -> Minimap.

Minimap will show each mark text for fast orientation in code. Each mark is written like // MARK: Variables

Answer 16

//MARK: does not seem to work for me in Xcode 6.3.2. However, this is what I did to get it to work:

1) Code:

import Cocoa

class MainWindowController: NSWindowController {

    //MARK: - My cool methods

    func fly() {
    }

    func turnInvisible() {

    }
}

2) In the jump bar nothing appears to change when adding the //MARK: comment. However, if I click on the rightmost name in the jump bar, in my case it says MainWindowController(with a leading C icon), then a popup window will display showing the effects of the //MARK: comment, namely a heading that says "My cool methods":

3) I also notice that if I click on one of the methods in my code, then the method becomes the rightmost entry in the jump bar. In order to get MainWindowController(with a leading C icon) to be the rightmost entry in the jump bar, I have to click on the whitespace above my methods.

Answer 17

Apple states in the latest version of Building Cocoa Apps,

The Swift compiler does not include a preprocessor. Instead, it takes advantage of compile-time attributes, build configurations, and language features to accomplish the same functionality. For this reason, preprocessor directives are not imported in Swift.

The # character appears to still be how you work with various build configurations and things like that, but it looks like they're trying to cut back on your need for most preprocessing in the vein of pragma and forward you to other language features altogether. Perhaps this is to aid in the operation of the Playgrounds and the REPL behaving as close as possible to the fully compiled code.

Answer 18

Pragma mark is a way to improve the readability of your code. The pragma comments would appear like tags on the Xcode jumpbar.

//MARK:  <Your comment goes here>

Example: In the code,

//MARK: Properties

// MARK: View Life cycle

//MARK: Helper methods

This is how it would appear in the Xcode jump bar.

Answer 19

Add a to-do item: Insert a comment with the prefix TODO:. For example: // TODO: [your to-do item].

Add a bug fix reminder: Insert a comment with the prefix FIXME:. For example: // FIXME: [your bug fix reminder].

Add a heading: Insert a comment with the prefix MARK:. For example: // MARK: [your section heading].

Add a separator line: To add a separator above an annotation, add a hyphen (-) before the comment portion of the annotation. For example: // MARK: - [your content]. To add a separator below an annotation, add a hyphen (-) after the comment portion of the annotation. For example: // MARK: [your content] -.

Answer 20

Try this:

// MARK: Reload TableView

func reloadTableView(){

    tableView.reload()
}