StringBuilder

A fast and low allocation StringBuilder for .NET.

Getting Started

Install the package:

PM> Install-Package LinkDotNet.StringBuilder

Afterward, use the package as follow:

using LinkDotNet.StringBuilder; // Namespace of the package

using ValueStringBuilder stringBuilder = new();
stringBuilder.AppendLine("Hello World");

string result = stringBuilder.ToString();

There are also smaller helper functions, which enable you to use ValueStringBuilder without any instance:

string result1 = ValueStringBuilder.Concat("Hello ", "World"); // "Hello World"
string result2 = ValueStringBuilder.Concat("Hello", 1, 2, 3, "!"); // "Hello123!"

By default, ValueStringBuilder uses a rented buffer from ArrayPool<char>.Shared. You can avoid renting overhead with an initially stack-allocated buffer:

using ValueStringBuilder stringBuilder = new(stackalloc char[128]);

Note that this will prevent you from returning stringBuilder or assigning it to an out parameter.

What does it solve?

The dotnet version of the StringBuilder is an all-purpose version that normally fits a wide variety of needs. But sometimes, low allocation is key. Therefore I created the ValueStringBuilder. It is not a class but a ref struct that tries to allocate as little as possible. If you want to know how the ValueStringBuilder works and why it uses allocations and is even faster, check out this blog post. The blog goes into a bit more in detail about how it works with a simplistic version of the ValueStringBuilder.

What doesn't it solve?

The library is not meant as a general replacement for the StringBuilder built into .NET. You can head over to the documentation and read about the "Known limitations". The library works best for a small to medium length strings (not hundreds of thousands of characters, even though it can be still faster and performs fewer allocations). At any time, you can convert the ValueStringBuilder to a "normal" StringBuilder and vice versa.

The normal use case is to concatenate strings in a hot path where the goal is to put as minimal pressure on the GC as possible.

Documentation

More detailed documentation can be found here. It is really important to understand how the ValueStringBuilder works so that you did not run into weird situations where performance/allocations can even rise.

Benchmark

The following table compares the built-in StringBuilder and this library's ValueStringBuilder:

BenchmarkDotNet v0.14.0, macOS Sequoia 15.3.1 (24D70) [Darwin 24.3.0]
Apple M2 Pro, 1 CPU, 12 logical and 12 physical cores
.NET SDK 9.0.200
  [Host]     : .NET 9.0.2 (9.0.225.6610), Arm64 RyuJIT AdvSIMD
  DefaultJob : .NET 9.0.2 (9.0.225.6610), Arm64 RyuJIT AdvSIMD


| Method              | Mean      | Error    | StdDev   | Ratio | Gen0   | Allocated | Alloc Ratio |
|-------------------- |----------:|---------:|---------:|------:|-------:|----------:|------------:|
| DotNetStringBuilder | 126.74 ns | 0.714 ns | 0.667 ns |  1.00 | 0.1779 |    1488 B |        1.00 |
| ValueStringBuilder  |  95.69 ns | 0.118 ns | 0.110 ns |  0.76 | 0.0669 |     560 B |        0.38 |

For more comparisons, check the documentation.

Another benchmark shows that ValueStringBuilder allocates less memory when appending value types (such as int and double):

| Method                         | Mean     | Error   | StdDev  | Gen0   | Gen1   | Allocated |
|------------------------------- |---------:|--------:|--------:|-------:|-------:|----------:|
| ValueStringBuilderAppendFormat | 821.7 ns | 1.29 ns | 1.14 ns | 0.4330 |      - |   3.54 KB |
| StringBuilderAppendFormat      | 741.5 ns | 5.58 ns | 5.22 ns | 0.9909 | 0.0057 |    8.1 KB |

Check out the Benchmark for a more detailed comparison and setup.

Support & Contributing

Thanks to all contributors and people that are creating bug-reports and valuable input: