Singleton

Namespace: DesignPatterns.Creational

Attribute

[GenerateSingleton] on a sealed partial class with a parameterless constructor. The generator emits Lazy<T> backing and a static Instance property.

[GenerateSingleton]
public sealed partial class AppSettings
{
    public string AppName { get; init; } = "Demo";
}

// Generated: AppSettings.Instance

Async initialization

Set InitializeAsync to the name of a static initializer returning Task or ValueTask. The generator validates the signature and emits GetInstanceAsync() instead of the synchronous Instance property.

[GenerateSingleton(InitializeAsync = nameof(InitializeAsync))]
public sealed partial class AppSettings
{
    public bool IsInitialized { get; private set; }

    public static ValueTask InitializeAsync(
        AppSettings instance,
        CancellationToken cancellationToken)
    {
        instance.IsInitialized = true;
        return ValueTask.CompletedTask;
    }
}

var settings = await AppSettings.GetInstanceAsync();

Diagnostics

• DP001 — type must be partial
• DP002 — invalid target shape
• DP067 — async initializer has an invalid signature
• DP068 — generated Singleton is also registered as a DI Singleton
• DP069 — non-thread-safe generated Singleton contains mutable instance state
• DP070 — mutable static Singleton candidate
• DP071 — mutable static Singleton is also registered as a DI Singleton

Sample

DesignPatterns.Samples.GenerateSingleton

Maintainer notes

Full design doc (中文): DesignPatterns/docs — see repository README for Singleton row in the patterns table.