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Zero Allocation StringBuilder for .NET Core and Unity.

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"x:" + x + " y:" + y + " z:" + z is converted to String.Concat(new []{ "x:", x.ToString(), " y:", y.ToString(), " z:", z.ToString() }) by C# compiler. It has each .ToString allocation and params array allocation. string.Format calls String.Format(string, object, object, object) so each arguments causes int -> object boxing.

All ZString methods only allocate final string. Also, ZString has enabled to access inner buffer so if output target has stringless api(like Unity TextMeshPro's SetCharArray), you can achieve completely zero allocation.

The blog post of detailed explanation by author: medium@neuecc/ZString

Related project for loggin using with ZString, Cysharp/ZLogger - Zero Allocation Text/Strcutured Logger.

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Table of Contents

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Getting Started

For .NET Core, use NuGet.

PM> Install-Package ZString

For Unity, check the releases page, download ZString.Unity.unitypackage.

using Cysharp.Text; // namespace

async void Example(int x, int y, int z)
{
    // same as x + y + z
    _ = ZString.Concat(x, y, z);

    // also can use numeric format strings
    _ = ZString.Format("x:{0}, y:{1:000}, z:{2:P}",x, y, z);

    _ = ZString.Join(',', x, y, z);

    // for Unity, direct write(avoid string allocation completely) to TextMeshPro
    tmp.SetTextFormat("Position: {0}, {1}, {2}", x, y, z);

    // create StringBuilder
    using(var sb = ZString.CreateStringBuilder())
    {
        sb.Append("foo");
        sb.AppendLine(42);
        sb.AppendFormat("{0} {1:.###}", "bar", 123.456789);

        // and build final string
        var str = sb.ToString();

        // for Unity, direct write to TextMeshPro
        tmp.SetText(sb);

        // write to destination buffer
        sb.TryCopyTo(dest, out var written);
    }

    // prepare format, return value should store to field(like RegexOptions.Compile)
    var prepared = ZString.PrepareUtf16<int, int>("x:{0}, y:{1:000}");
    _ = prepared.Format(10, 20);

    // C# 8.0, Using declarations
    // create Utf8 StringBuilder that build Utf8 directly to avoid encoding
    using var sb2 = ZString.CreateUtf8StringBuilder();

    sb2.AppendFormat("foo:{0} bar:{1}", x, y);

    // directly write to steam or dest to avoid allocation
    await sb2.WriteToAsync(stream);
    sb2.CopyTo(bufferWritter);
    sb2.TryCopyTo(dest, out var written);
}

Reference

static class ZString

methodreturnsdescription
CreateStringBuilder()Utf16ValueStringBuilderCreate the Utf16 string StringBuilder.
CreateStringBuilder(bool notNested)Utf16ValueStringBuilderCreate the Utf16 string StringBuilder, when true uses thread-static buffer that is faster but must return immediately.
CreateUtf8StringBuilder()Utf8ValueStringBuilderCreate the Utf8(Span<byte>) StringBuilder.
CreateUtf8StringBuilder(bool notNested)Utf8ValueStringBuilderCreate the Utf8(Span<byte>) StringBuilder, when true uses thread-static buffer that is faster but must return immediately.
Join(char/string, T[]/IE<T>)stringConcatenates the elements of an array, using the specified seperator between each element.
PrepareUtf16<T1,..,T16>(string)Utf16PreparedFormat<T1,...,T16>Prepare string format to avoid parse template in each operation.
PrepareUtf8<T1,..,T16>(string)Utf8PreparedFormat<T1,...,T16>Prepare string format to avoid parse template in each operation.
Concat<T1,..,T16>(T1,..,T16)stringConcatenates the string representation of some specified values.
Format<T1,..,T16>(string, T1,..,T16)stringReplaces one or more format items in a string with the string representation of some specified values.
Utf8Format<T1,..,T16>(IBufferWriter<byte>, T1,..,T16)voidReplaces one or more format items in a string with the string representation of some specified values.

struct Utf16ValueStringBuilder : IBufferWriter<char>, IDisposable

methodreturnsdescription
LengthintLength of written buffer.
AsSpan()ReadOnlySpan<char>Get the written buffer data.
AsMemory()ReadOnlyMemory<char>Get the written buffer data.
AsArraySegment()ArraySegment<char>Get the written buffer data.
Dispose()voidReturn the inner buffer to pool.
Append<T>(T value)voidAppends the string representation of a specified value to this instance.
Append<T>(T value, string format)voidAppends the string representation of a specified value to this instance with numeric format strings.
AppendJoin(char/string, T[]/IE<T>)voidConcatenates and appends the elements of an array, using the specified seperator between each element.
AppendLine()voidAppends the default line terminator to the end of this instance.
AppendLine<T>(T value)voidAppends the string representation of a specified value followed by the default line terminator to the end of this instance.
AppendLine<T>(T value, string format)voidAppends the string representation of a specified value with numeric format strings followed by the default line terminator to the end of this instance.
AppendFormat<T1,..,T16>(string, T1,..,T16)voidAppends the string returned by processing a composite format string, each format item is replaced by the string representation of arguments.
TryCopyTo(Span<char>, out int)boolCopy inner buffer to the destination span.
ToString()stringConverts the value of this instance to a System.String.
GetMemory(int sizeHint)Memory<char>IBufferWriter.GetMemory.
GetSpan(int sizeHint)Span<char>IBufferWriter.GetSpan.
Advance(int count)voidIBufferWriter.Advance.
static RegisterTryFormat<T>(TryFormat<T>)voidRegister custom formatter.

struct Utf8ValueStringBuilder : IBufferWriter<byte>, IDisposable

methodreturnsdescription
LengthintLength of written buffer.
AsSpan()ReadOnlySpan<char>Get the written buffer data.
AsMemory()ReadOnlyMemory<char>Get the written buffer data.
AsArraySegment()ArraySegment<char>Get the written buffer data.
Dispose()voidReturn the inner buffer to pool.
Append<T>(T value)voidAppends the string representation of a specified value to this instance.
Append<T>(T value, StandardFormat format)voidAppends the string representation of a specified value to this instance with numeric format strings.
AppendJoin(char/string, T[]/IE<T>)voidConcatenates and appends the elements of an array, using the specified seperator between each element.
AppendLine()voidAppends the default line terminator to the end of this instance.
AppendLine<T>(T value)voidAppends the string representation of a specified value followed by the default line terminator to the end of this instance.
AppendLine<T>(T value, StandardFormat format)voidAppends the string representation of a specified value with numeric format strings followed by the default line terminator to the end of this instance.
AppendFormat<T1,..,T16>(string, T1,..,T16)voidAppends the string returned by processing a composite format string, each format item is replaced by the string representation of arguments.
CopyTo(IBufferWriter<byte>)voidCopy inner buffer to the buffer writer.
TryCopyTo(Span<byte>, out int)boolCopy inner buffer to the destination span.
WriteToAsync(Stream stream)TaskWrite inner buffer to stream.
ToString()stringEncode the innner utf8 buffer to a System.String.
GetMemory(int sizeHint)Memory<char>IBufferWriter.GetMemory.
GetSpan(int sizeHint)Span<char>IBufferWriter.GetSpan.
Advance(int count)voidIBufferWriter.Advance.
static RegisterTryFormat<T>(TryFormat<T>)voidRegister custom formatter.

class Utf16PreparedFormat<T1,..,T16>

methodreturnsdescription
FormatstringReplaces one or more format items in a string with the string representation of some specified values.
FormatTo<TBufferWriter>(ref TBufferWriter, T1,..,T16)voidReplaces one or more format items in a string with the string representation of some specified values.

class Utf8PreparedFormat<T1,..,T16>

methodreturnsdescription
FormatstringReplaces one or more format items in a string with the string representation of some specified values.
FormatTo<TBufferWriter>(ref TBufferWriter, T1,..,T16)voidReplaces one or more format items in a string with the string representation of some specified values.

class ZStringWriter : TextWriter

A TextWriter implementation that is backed with Utf16ValueStringBuilder
It's important to make sure the writer is always properly disposed.

static class TextMeshProExtensions(Unity only)

methodreturnsdescription
SetText(Utf16ValueStringBuilder)voidSet inner buffer to text mesh pro directly to avoid string allocation.
SetTextFormat<T1,..,T16>(string, T1,..,T16)voidSet formatted string without string allocation.

Unity

Install via UPM git URL package or asset package(ZString...*.unitypackage) available in ZString/releases page.

If you want to set a target version, ZString uses the *.*.* release tag so you can specify a version like #2.4.0. For example https://github.com/Cysharp/ZString.git?path=src/ZString.Unity/Assets/Scripts/ZString#2.4.0.

Supporting minimum Unity version is 2021.3. The dependency managed DLL System.Runtime.CompilerServices.Unsafe/6.0.0 is included with unitypackage. For git references, you will need to add them in another way as they are not included to avoid unnecessary dependencies; either extract the dll from unitypackage or download it from the NuGet page.

TextMeshPro support is automatically enabled when importing the com.unity.textmeshpro package from package manager. (If you do not use the package manager, define the scripting define symbol ZSTRING_TEXTMESHPRO_SUPPORT to enable it.)

Advanced Tips

ZString.CreateStringBuilder(notNested:true) is a special optimized parameter that uses ThreadStatic buffer instead of rent from ArrayPool. It is slightly faster but can not use in nested.

using(var sb = ZString.CreateStringBuilder(true))
{
    sb.Append("foo");

    using var sb2 = ZString.CreateStringBuilder(true); // NG, nested stringbuilder uses conflicted same buffer
    var str = ZString.Concat("x", 100); // NG, ZString.Concat/Join/Format uses threadstatic buffer
}
// OK, return buffer immediately.
using(var sb = ZString.CreateStringBuilder(true))
{
    sb.Append("foo");
    return sb.ToString();
}

ZString.CreateStringBuilder() is same as ZString.CreateStringBuilder(notNested:false).


In default, SByte, Int16, Int32, Int64, Byte, UInt16, UInt32, UInt64, Single, Double, TimeSpan, DateTime, DateTimeOffset, Decimal, Guid, String, Char are used there own formatter to avoid .ToString() allocation, write directly to buffer. If not exists there list type, used .ToString() and copy string data.

If you want to avoid to convert string in custom type, you can register your own formatter.

Utf16ValueStringBuilder.RegisterTryFormat((MyStruct value, Span<char> destination, out int charsWritten, ReadOnlySpan<char> format) =>
{
    // write value to destionation and set size to charsWritten.
    charsWritten = 0;
    return true;
});

Utf8ValueStringBuilder.RegisterTryFormat((MyStruct value, Span<byte> destination, out int written, StandardFormat format) =>
{
    written = 0;
    return true;
});

CreateStringBuilder and CreateUtf8StringBuilder must use with using. Because their builder rent 64K buffer from ArrayPool. If not return buffer, allocate 64K buffer when string builder is created.


Utf16ValueStringBuilder and Utf8ValueStringBuilder are mutable struct, be careful to copy by passing method. Use ref and try-finally.

void Build()
{
    var sb = ZString.CreateStringBuilder();
    try
    {
        BuildHeader(ref sb);
        BuildMessage(ref sb);
    }
    finally
    {
        // when use with `ref`, can not use `using`.
        sb.Dispose();
    }
}


void BuildHeader(ref Utf16ValueStringBuilder builder)
{
    //..
}

void BuildMessage(ref Utf16ValueStringBuilder builder)
{
    //..
}

Utf8Format, Utf8StringBuilder uses Utf8Formatter.TryFormat and there format string is not same as standard format. It uses StandardFormat, combinate of symbol char and precision. Supported format string symbol can find in Utf8Formatter.TryFormat document(For example Int32 supports G, D, N, X and Boolean supports G, I). Precision(zero padding) can pass after symbol like D2. For example sb.AppendFormat("{0:D2}:{1:D2}:{2:D2}", hour, minute, second).

TryFormat(DateTime) and TryFormat(TimeSpan) symbol is too restricted than standard string format. If you want to use custom format, deconstruct there Day, Hour, etc.


Utf8ValueStringBuilder and Utf16ValueStringBuilder implements IBufferWriter so you can pass serializer(such as JsonSerializer of System.Text.Json). But be careful to boxing copy, ValueStringBuilder is mutable struct. For example,

using var sb = ZString.CreateUtf8StringBuilder();
IBufferWriter<byte> boxed = sb;
var writer = new Utf8JsonWriter(boxed);
JsonSerializer.Serialize(writer, ....);

using var unboxed = (Utf8ValueStringBuilder)boxed;
var str = unboxed.ToString();

License

This library is licensed under the MIT License.

.NET Standard 2.0 and Unity version borrows dotnet/runtime conversion methods, there exists under ZString/Number directory. This third-party license follows runtime/LICENSE.TXT.