TextApi

Diff

TextDiff computes the minimum edit script between two texts using the Myers O(ND) algorithm. Results come as structured DiffHunk lists, character-level DiffSpan sequences, or rendered unified-diff strings.

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TextDocument

Examples

Advanced

Quick Reference

using TextAPI.Core.Diff;

// Line-level diff of two strings
DiffResult result = TextDiff.Diff(oldText, newText);

Console.WriteLine($"+{result.AddedLines} / -{result.DeletedLines}");
Console.WriteLine(result.ToUnifiedDiff());

// Character-level diff
var spans = TextDiff.DiffChars("Hello World", "Hello TextAPI");
foreach (var s in spans)
	Console.WriteLine($"{s.Kind}: \"{s.Text}\"");

TextDiff Static Methods

Method	Returns	Description
Diff(string old, string new, opts?)	DiffResult	Line-level diff of two strings.
Diff(string[] old, string[] new, opts?)	DiffResult	Line-level diff of pre-split line arrays.
Diff(TextDocument old, TextDocument new, opts?)	DiffResult	Line-level diff of two documents.
DiffChars(string old, string new)	IReadOnlyList<DiffSpan>	Character-level diff.

DiffOptions

Property	Type	Default	Description
IgnoreCase	bool	false	Treat uppercase and lowercase as equal.
IgnoreWhitespace	bool	false	Trim and collapse runs of whitespace before comparing.
MaxEditDistance	int	int.MaxValue	Abort if edit distance exceeds this. Returns partial result.

var opts = new DiffOptions
{
	IgnoreCase       = true,
	IgnoreWhitespace = true
};

DiffResult r = TextDiff.Diff(a, b, opts);

// Or use the defaults
DiffResult r2 = TextDiff.Diff(a, b, DiffOptions.Default);

DiffResult

Property	Type	Description
Hunks	IReadOnlyList<DiffHunk>	All hunks in document order.
AddedLines	int	Total lines inserted across all hunks.
DeletedLines	int	Total lines deleted across all hunks.
HasChanges	bool	True when the two texts differ.
ToUnifiedDiff(old?, new?, ctx?)	string	Render as unified diff. Default 3 context lines.

DiffHunk

Property	Type	Description
Kind	DiffKind	Equal, Insert, or Delete.
OldStart	int	Zero-based start line in the old document.
OldCount	int	Number of lines from the old document.
NewStart	int	Zero-based start line in the new document.
NewCount	int	Number of lines from the new document.
Lines	IReadOnlyList<string>	Line content for this hunk.

DiffKind Enum

Value	Meaning
Equal	Lines are the same in both versions.
Insert	Lines were added in the new version.
Delete	Lines were removed from the old version.

DiffSpan (Character-Level)

readonly record struct DiffSpan(DiffKind Kind, string Text);

Each DiffSpan is a contiguous run of equal, inserted, or deleted characters. Use this for inline diff rendering in a UI:

var spans = TextDiff.DiffChars("the cat sat", "the bat sat");
// Equal:"the ", Delete:"c", Insert:"b", Equal:"at sat"

foreach (var s in spans)
{
	string prefix = s.Kind switch
	{
		DiffKind.Insert => "+",
		DiffKind.Delete => "-",
		_               => " "
	};
	Console.Write($"{prefix}{s.Text}");
}

Unified Diff Output

var result = TextDiff.Diff(oldText, newText);

// Default: 3 context lines, paths "a" and "b"
string patch = result.ToUnifiedDiff();

// Custom paths and context
string patch2 = result.ToUnifiedDiff(
	oldPath:      "original/file.cs",
	newPath:      "modified/file.cs",
	contextLines: 5
);

Output format:

--- original/file.cs
+++ modified/file.cs
@@ -1,4 +1,4 @@
 line 1
-old line
+new line
 line 3

Iterating Hunks

var result = TextDiff.Diff(oldDoc, newDoc);

foreach (var hunk in result.Hunks.Where(h => h.Kind != DiffKind.Equal))
{
	string symbol = hunk.Kind == DiffKind.Insert ? "+" : "-";
	foreach (var line in hunk.Lines)
		Console.WriteLine($"{symbol} {line}");
}

Performance Notes

• Uses the Myers O(ND) algorithm — optimal for typical source code diffs.
• MaxEditDistance can be used to cap cost on very large or wildly different files.
• Character-level diff (DiffChars) is best for single words or short lines. For long texts prefer line-level diff first, then character diff per changed line.