Soenneker.Utils.PooledStringBuilders

Tiny, fast ref struct string builder. Backed by ArrayPool<char>. Low allocations. Short-lived use.

Installation

dotnet add package Soenneker.Utils.PooledStringBuilders

Example

using Soenneker.Utils.PooledStringBuilders;

using var sb = new PooledStringBuilder(128);

sb.Append("Hello, ");
sb.Append(name);
sb.Append(' ');
sb.Append(id);        // ISpanFormattable path, no boxing
sb.AppendLine();

string s = sb.ToString(); // creates a string; using returns the buffer afterward

Use ToString() when the builder remains in scope and will be disposed separately. For a one-shot finish without a using declaration:

var sb = new PooledStringBuilder();
sb.Append("value=");
sb.Append(value);

string result = sb.ToStringAndDispose();

Cheatsheet

• new PooledStringBuilder(int capacity = 128)
• Append(char), Append(string?), Append(ReadOnlySpan<char>)
• Append<T>(T value, ReadOnlySpan<char> format = default, IFormatProvider? provider = null) where T : ISpanFormattable
• AppendSpan(int length) — reserve and write directly into the buffer
• Insert(...), Shrink(int), AppendLine(...), AppendSeparatorIfNotEmpty(char)
• Length, Capacity, AsSpan(), EnsureCapacity(int), Clear()
• ToString() — create a string without disposing the builder
• ToStringAndDispose(bool clear = false) — create a string and return the buffer
• Dispose() / Dispose(bool clear)

Notes

• PooledStringBuilder is a stack-only ref struct; it cannot be boxed, captured, stored in a normal field, or kept across await.
• Do not copy the builder (var copy = builder). Copies refer to the same rented array and can return it to the pool more than once. Pass it by ref when a helper must mutate the same builder.
• Dispose exactly once, either through using, Dispose, or ToStringAndDispose. Do not use ToStringAndDispose and then dispose a copied or aliased value.
• AppendSpan(length) immediately increases Length and returns uninitialized pooled storage. Fill the entire span before reading or converting the builder, or previous pool contents could appear in the result.
• AsSpan() is valid only until the builder grows, changes, or is disposed. Do not retain it.
• AppendLine appends \n, not Environment.NewLine.
• Clear() resets the logical length but does not zero the array. Use Dispose(clear: true) or ToStringAndDispose(clear: true) when the pooled buffer contained secrets. The returned managed string is still immutable and cannot be securely erased.
• The builder is not thread-safe. Keep it short-lived and confined to one synchronous scope.