SwiftDiff

SwiftDiff is a (partial) port of the Google Diff, Match and Patch Library (google-diff-match-patch) to Swift. The Google Diff, Match and Patch Library was originally written by Neil Fraser.

So far only the diff algorithm has been ported. It allows comparing two blocks of plain text and efficiently returning a list of their differences. It supports detecting in-line text differences.

License

SwiftDiff is licensed under the Apache License 2.0 – see the LICENSE file for details.

The original Google Diff, Match and Patch Library is also licensed under the same license and Copyright (c) 2006 Google Inc.

Usage

Basic Diff

diff(text1: "The quick brown fox jumps over the lazy dog.", 
     text2: "That quick brown fox jumped over a lazy dog.")

Returns an array of Diff objects:

[
  Diff(operation: .equal, text: "Th"),
  Diff(operation: .delete, text: "e"),
  Diff(operation: .insert, text: "at"),
  Diff(operation: .equal, text: " quick brown fox jump"),
  Diff(operation: .delete, text: "s"),
  Diff(operation: .insert, text: "ed"),
  Diff(operation: .equal, text: " over "),
  Diff(operation: .delete, text: "the"),
  Diff(operation: .insert, text: "a"),
  Diff(operation: .equal, text: " lazy dog.")
]

Diff with Indices

The diffWithIndices function returns IndexedDiff objects that include the exact positions where each diff operation occurs:

let text1 = "Hello World"
let text2 = "Hello Swift"
let diffs = diffWithIndices(text1: text1, text2: text2)

// Returns array of IndexedDiff objects:
// [
//   IndexedDiff(operation: .equal, text: "Hello ", startIndex: <index>, endIndex: <index>),
//   IndexedDiff(operation: .delete, text: "World", startIndex: <index>, endIndex: <index>),
//   IndexedDiff(operation: .insert, text: "Swift", startIndex: <index>, endIndex: <index>)
// ]

// For each IndexedDiff:
// - Equal and Delete operations: startIndex and endIndex refer to positions in text1
// - Insert operations: startIndex and endIndex (same value) refer to the position in text2

API Reference

Diff Types

// Basic diff result without indices
struct Diff {
    let operation: Operation
    let text: String
}

// Diff result with string indices
struct IndexedDiff {
    let operation: Diff.Operation
    let text: String
    let startIndex: String.Index
    let endIndex: String.Index
}

// Diff operations
enum Operation {
    case equal
    case insert
    case delete
}

Creating Diff Objects

// Basic Diff convenience methods
let equalDiff = Diff.equal("text")
let insertDiff = Diff.insert("new text")
let deleteDiff = Diff.delete("old text")

// IndexedDiff convenience methods
let indexedEqual = IndexedDiff.equal("text", startIndex: start, endIndex: end)
let indexedInsert = IndexedDiff.insert("new text", at: insertionPoint)
let indexedDelete = IndexedDiff.delete("old text", startIndex: start, endIndex: end)

Examples

Working with Multiple Languages

SwiftDiff correctly handles Unicode text including emoji, combining characters, and various scripts:

// Chinese
let diffs = diffWithIndices(text1: "你好世界", text2: "你好宇宙")

// Japanese
let diffs = diffWithIndices(text1: "こんにちは世界", text2: "こんばんは世界")

// Arabic (RTL)
let diffs = diffWithIndices(text1: "مرحبا بالعالم", text2: "مرحبا بالكون")

// Emoji and mixed scripts
let diffs = diffWithIndices(text1: "Hello 👋 World 🌍", text2: "Hello 👋 Swift 🚀")