Flint is a lightweight, zero-dependency C# library that provides fast text matching utilities using the Aho-Corasick algorithm.

Usage Examples

Basic

using Flint;

var matcher = new TextMatcher(new[] { "cat", "dog" });
var results = matcher.Find("The dog chased the cat.");

foreach (var match in results)
{
    Console.WriteLine($"Found '{match.Value}' at index {match.StartIndex}.");
}

Output:

Found 'dog' at index 4.
Found 'cat' at index 19.

An optional StringComparison can be passed to TextMatcher, influencing it's behavior when performing searches/replacement. If none is given, it will default to StringComparison.CurrentCulture.

using Flint;

var matcher = new TextMatcher(new[] { "cat", "dog" }, StringComparison.OrdinalIgnoreCase);
var results = matcher.Find("The DOG chased the CaT.");

foreach (var match in results)
{
    Console.WriteLine($"Found '{match.Value}' at index {match.StartIndex}.");
}

Output:

Found 'DOG' at index 4.
Found 'CaT' at index 19.

Find with a callback

TextMatcher provides an overload of Find that accepts a callback invoked for each match. This can be convenient to process matches as they are found without allocating a results collection.

using Flint;

var matcher = new TextMatcher(new[] { "cat", "dog" });
matcher.Find("The dog chased the cat.", match =>
{
    Console.WriteLine($"Found '{match.Value}' at index {match.StartIndex}.");
});

Output:

Found 'dog' at index 4.
Found 'cat' at index 19.

Scan multiple texts with FindAll

using Flint;

var patterns = new[] { "cat", "dog", "bird" };
var matcher = new TextMatcher(patterns);

var texts = new[]
{
    "The dog chased the cat.",
    "A bird watched them from above.",
    "No animals here."
};

var all = matcher.FindAll(texts);

foreach (var kv in all)
{
    Console.WriteLine(kv.Key);
    foreach (var m in kv.Value)
    {
        Console.WriteLine($"Found '{m.Value}' at index {m.StartIndex}.");
    }
}

Example output:

The dog chased the cat.
Found 'cat' at index 19.
Found 'dog' at index 4.
A bird watched them from above.
Found 'bird' at index 2.
No animals here.

If you need to scan many input strings and handle matches as they are discovered, use the FindAll overload that accepts an Action<string, Match> callback. The callback receives the original text and the match.

using Flint;

var patterns = new[] { "cat", "dog" };
var matcher = new TextMatcher(patterns);

var texts = new[]
{
    "The dog chased the cat.",
    "A bird watched from above.",
};

matcher.FindAll(texts, (text, match) =>
{
    Console.WriteLine(text);
    Console.WriteLine($"Found '{match.Value}' at index {match.StartIndex}.");
});

Example output:

The dog chased the cat.
Found 'dog' at index 4.
The dog chased the cat.
Found 'cat' at index 19.
A bird watched from above.

Exact (whole-word) matching with MatchMode

The MatchMode enum lets you require matches to be whole words. This prevents short patterns from matching inside longer words (for example, preventing "he" from matching inside "she").

using Flint;

var patterns = new[] { "he", "she" };
var matcher = new TextMatcher(patterns, StringComparison.CurrentCulture, MatchMode.ExactMatch);

var results = matcher.Find("she sells seashells.");

foreach (var m in results)
{
    Console.WriteLine($"Found '{m.Value}' at index {m.StartIndex}.");
}

Output (only the whole-word she is matched):

Found 'she' at index 0.

Overlapping and nested matches

using Flint;

var matcher = new TextMatcher(new[] { "he", "she", "his", "hers" });
var results = matcher.Find("she is his hero");

foreach (var m in results)
{
    Console.WriteLine($"Found '{m.Value}' at index {m.StartIndex}.");
}

Example output:

Found 'she' at index 0.
Found 'he' at index 1.
Found 'his' at index 7.
Found 'he' at index 10.

Replace all matches with a single value

using Flint;

var matcher = new TextMatcher(new[] { "cat", "dog" });
var replaced = matcher.Replace("The dog chased the cat.", "animal");
Console.WriteLine(replaced);

Output:

The animal chased the animal.

Replace matches using a function

using Flint;

var matcher = new TextMatcher(new[] { "cat", "dog" });
var replaced = matcher.Replace(
    "The dog chased the cat.",
    match => match.Value.ToUpper()
);
Console.WriteLine(replaced);

Output:

The DOG chased the CAT.

Replace each pattern with a different value

using Flint;

var matcher = new TextMatcher(new[] { "cat", "dog" });
var replaced = matcher.Replace(
    "The dog chased the cat.",
    new[] { "feline", "canine" }
);
Console.WriteLine(replaced);

Output:

The canine chased the feline.

Load patterns from a file

using Flint;

var patterns = File.ReadAllLines("patterns.txt")
                   .Where(l => !string.IsNullOrWhiteSpace(l));

var matcher = new TextMatcher(patterns);

var text = File.ReadAllText("large_input.txt");
var hits = matcher.Find(text).ToArray();

Console.WriteLine($"Found {hits.Length} matches.");

Support

• .NET Standard 2.0 and .NET 8.0

License

Flint is licensed under the MIT License.