Object Pool

Object Pool keeps reusable, expensive objects behind explicit leases. PatternKit's runtime API is thread-safe, bounded, and designed for services that need temporary buffers, protocol clients, encoders, or other resettable resources without allocating on every operation.

var pool = ObjectPool<FormulaEvaluationBuffer>
    .Create()
    .WithFactory(static () => new FormulaEvaluationBuffer())
    .OnReturn(static buffer => buffer.Reset())
    .WithMaxRetained(16)
    .Build();

using var lease = pool.Rent();
lease.Value.Load(variables);
var total = lease.Value.Evaluate("subtotal + tax");

Use OnReturn to reset state, RetainWhen to discard unhealthy instances, and WithMaxRetained to prevent unbounded memory growth. Disposing the lease returns the object exactly once. Disposing the pool releases retained IDisposable instances.

Source Generation

[GenerateObjectPool(
    typeof(FormulaEvaluationBuffer),
    FactoryMethodName = "CreateGenerated",
    MaxRetained = 16,
    ResetMethodName = nameof(FormulaEvaluationBuffer.Reset))]
public static partial class SpreadsheetFormulaBufferPools;

The generated factory emits the same fluent API calls as handwritten code. It validates that the pool host is partial and that the pooled type can be constructed with new T().

Dependency Injection

Register the generated pool as a singleton and inject it into services that rent buffers per operation:

services.AddSingleton(static _ => SpreadsheetFormulaBufferPools.CreateGenerated());
services.AddSingleton<SpreadsheetFormulaService>();

The spreadsheet formula demo in src/PatternKit.Examples/ObjectPoolDemo shows the production shape with IServiceCollection, a generated route, and TinyBDD coverage.