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https://github.com/mcudich/HeckelDiff

A fast Swift diffing library.
https://github.com/mcudich/HeckelDiff

batched-updates diffing swift uicollectionviews

Last synced: 3 months ago
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A fast Swift diffing library.

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README 

        
# HeckelDiff

[![Swift](https://img.shields.io/badge/swift-3-orange.svg?style=flat)](#)

[![Carthage compatible](https://img.shields.io/badge/Carthage-compatible-4BC51D.svg?style=flat)](https://github.com/Carthage/Carthage)

[![CocoaPods Compatible](https://img.shields.io/cocoapods/v/HeckelDiff.svg)](https://img.shields.io/cocoapods/v/HeckelDiff)

[![Platform](https://img.shields.io/cocoapods/p/HeckelDiff.svg?style=flat)](http://cocoadocs.org/docsets/HeckelDiff)

[![License](https://img.shields.io/badge/license-MIT-blue.svg?style=flat)](https://opensource.org/licenses/MIT)



Pure Swift implementation of Paul Heckel's *A Technique for Isolating Differences Between Files*



## Features



This is a simple diff algorithm that provides the minimum set of steps to transform one collection into another. Transformations are listed as discrete operations:

* **Insertion** - what items should be inserted into the array, and at what index.

* **Deletion** - what items should be removed from the array, and at what index.

* **Move** - what items should be moved, and their origin and destination indices.

* **Update** - what items should be updated/replaced with new context, and at what index.



These operations are calculated in **linear** time, using the algorithm described in [this paper](http://dl.acm.org/citation.cfm?id=359467).



Knowing this set of operations is especially handy for efficiently updating **UITableViews** and **UICollectionViews**.



## Example



Consider a simple example that compares lists of integers:

```swift

let o = [1, 2, 3, 3, 4]

let n = [2, 3, 1, 3, 4]

let result = diff(o, n)

// [.move(1, 0), .move(2, 1), .move(0, 2)]



let o = [0, 1, 2, 3, 4, 5, 6, 7, 8]

let n = [0, 2, 3, 4, 7, 6, 9, 5, 10]

let result = diff(o, n)

// [.delete(1), .delete(8), .move(7, 4), .insert(6), .move(5, 7), .insert(8)]

```



`orderedDiff` is also available, which provides a set of operations that are friendly for batched updates in UIKit contexts (note how `move` is replaced by pairs of `insert` and `delete` operations):

```swift

let o = [1, 2, 3, 3, 4]

let n = [2, 3, 1, 3, 4]

let result = orderedDiff(o, n)

// [.delete(2), .delete(1), .delete(0), .insert(0), .insert(1), .insert(2)]

```



## UITableView/UICollectionView Support



HeckelDiff has built-in support for generating efficient batched updates for `UITableView` and `UICollectionView`. Methods are made available on both that allow informing the corresponding table or collection view that their data model has changed.



For example:

```swift

tableView.applyDiff(previousItems, newItems, withAnimation: .fade)

```

or

```swift

collectionView.applyDiff(previousItems, newItems)

```



## Update Support



Elements in collections passed into `diff` must conform to `Hashable`. HeckelDiff uses elements' `hashValues` to determine whether they should be **inserted**, **deleted** or **moved**. In some cases, elements are instead marked for **update**. This is because even though the `hashValues` of two elements might be equivalent, the elements may not be **equal**. You can take advantage of this by implementing the `Hashable` protocol in such a way that your elements get updated when appropriate.



For example, you may have two records that refer to the same person (perhaps you use a record ID as a hash value). You may want to support a case where a person's phone number may change, but the record itself remains in the same position in the array. Your `Equatable` implementation may take the phone number value into account, whereas your `hashValue` may only reflect the underlying record ID value.



In the context of a `UITableView` or `UICollectionView`, you would most efficiently handle this by reloading the given row that needs updating (rather than deleting it and re-inserting it). Use the supplied `applyDiff` functions to have HeckelDiff perform this for you.



## Installation



#### Carthage



You can install Carthage with [Homebrew](http://brew.sh/) using the following command:



```bash

$ brew update

$ brew install carthage

```



Add the following line to your [Cartfile](https://github.com/Carthage/Carthage/blob/master/Documentation/Artifacts.md#cartfile):



```ogdl

github "mcudich/HeckelDiff"

```



Run `carthage update`, then make sure to add `HeckelDiff.framework` to "Linked Frameworks and Libraries" and "copy-frameworks" Build Phases.



#### CocoaPods



[CocoaPods](http://cocoapods.org) is a dependency manager for Cocoa projects. You can install it with the following command:



```bash

$ gem install cocoapods

```



To integrate TemplateKit into your Xcode project using CocoaPods, specify it in your `Podfile`:



```ruby

source 'https://github.com/CocoaPods/Specs.git'

platform :ios, '10.0'

use_frameworks!



target '' do

    pod 'HeckelDiff', '~> 0.1.0'

end

```



Then, run the following command:



```bash

$ pod install

```



## Requirements



- iOS 9.0+

- Xcode 8.0+

- Swift 3.0+