Split.net

A more efficient splitter for bytes and strings, with a focus on zero allocation, in C#.

Usage

dotnet add package SplitDotNet

var example = "Hello, 🌏 world. 你好, 世界. ";

var splits = example.SplitOn(" ");

foreach (var split in splits)
{
    // split is a ReadOnlySpan<char>
}

var bytes = Encoding.UTF8.GetBytes(example);
var separators = " ,."u8.ToArray();
var splits2 = bytes.SplitOnAny(separators);

foreach (var split2 in splits2)
{
    // split2 is a ReadOnlySpan<byte>
}

Performance

This package exists to save allocations on the hot path, if you are using something like strings.Split from the standard library. Benchmarks on ~100K of text:

| Method            | Mean      | Error    | StdDev   | Throughput | Gen0    | Gen1   | Gen2   | Allocated |
|------------------ |----------:|---------:|---------:|----------- |--------:|-------:|-------:|----------:|
| Split.net         |  91.68 us | 0.804 us | 0.712 us |  1.19 GB/s |       - |      - |      - |         - |

Standard library:

| Method            | Mean      | Error    | StdDev   | Throughput | Gen0    | Gen1   | Gen2   | Allocated |
|------------------ |----------:|---------:|---------:|----------- |--------:|-------:|-------:|----------:|
| string.Split      | 106.40 us | 0.138 us | 0.108 us |  1.02 GB/s | 49.3164 | 0.3662 | 0.1221 |  413352 B |

Techniques

This package does two things to achieve zero allocations. First, it lazily iterates over the splits, instead of collecting them into an array.

Second, each split is a Span, which is a "view" into the underlying string or byte[], and stays on the stack. Here's a blog post.

Data types

using Split.Extensions;

You will find .SplitOn() and .SplitOnAny() extension methods added to: string, byte[], char[], (ReadOnly)Span<char|byte>, Stream and TextReader/StreamReader .

using Split;

If you don't like all those extension methods hanging off your types:

You'll find Split.Bytes() and Split.BytesAny(), accepting byte[], (ReadOnly)Span<byte> and Stream.

You'll find Split.Chars() and Split.CharsAny(), which can accept string, char[], (ReadOnly)Span<char> and TextReader/StreamReader.

Testing

We test that Split.net returns identical results to string.Split, including various edge cases.

Prior art

These are not original ideas! Here are a few other examples with a similar approach:

• SpanSplitEnumerator (This Split.net package started as a fork of SpanSplitEnumerator)

• StringTokenizer

• StringExtensions.Tokenize

Each of the above is in the same ballpark of throughput and allocation as this package.

Why use Split.net, then?

You might like the UTF-8 support, SplitAny, streams & readers, or heck maybe you just like the API. Feedback welcome.

By the way

If you are splitting in order to get "words" from natural text, you may wish to use the Unicode definition of word boundaries, which I've implemented in this package.

I've also implemented these ideas in Go.