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Singleton Pattern

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Before: full revision: 2026-10-25 00:14:01 UTC After: full revision: 2026-10-25 02:09:41 UTC

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using System; using System.Collections.Generic; using System.Linq; Console.WriteLine(ReferenceEquals(AppCatalog.Instance, AppCatalog.Instance)); sealed class AppCatalog { private static readonly Lazy<AppCatalog> shared = new(() => new AppCatalog()); private AppCatalog() { } public static AppCatalog Instance => shared.Value; public string Version => "v1"; }

using System; using System.Collections.Generic; using System.Linq; Console.WriteLine(ReferenceEquals(AppCatalog.Instance, AppCatalog.Instance)); // Own construction so callers do not create separate catalogs. sealed class AppCatalog { private static readonly Lazy<AppCatalog> shared = new(() => new AppCatalog()); private AppCatalog() { } // Create on first synchronous access and reuse the object within this module instance. public static AppCatalog Instance => shared.Value; public string Version => "v1"; }

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using System; using System.Collections.Generic; using System.Linq; var tasks = Enumerable.Range(0, 8) .Select(_ => System.Threading.Tasks.Task.Run(() => AppCatalog.Instance)).ToArray(); var values = await System.Threading.Tasks.Task.WhenAll(tasks); Console.WriteLine(values.All(value => ReferenceEquals(value, values[0]))); Console.WriteLine(values[0].Version); sealed class AppCatalog { private static readonly Lazy<AppCatalog> shared = new(() => new AppCatalog()); private AppCatalog() { } public static AppCatalog Instance => shared.Value; public string Version => "v1"; }

using System; using System.Collections.Generic; using System.Linq; var tasks = Enumerable.Range(0, 8) .Select(_ => System.Threading.Tasks.Task.Run(() => AppCatalog.Instance)).ToArray(); var values = await System.Threading.Tasks.Task.WhenAll(tasks); Console.WriteLine(values.All(value => ReferenceEquals(value, values[0]))); Console.WriteLine(values[0].Version); // Own construction so callers do not create separate catalogs. sealed class AppCatalog { private static readonly Lazy<AppCatalog> shared = new(() => new AppCatalog()); private AppCatalog() { } // Create on first synchronous access and reuse the object within this module instance. public static AppCatalog Instance => shared.Value; public string Version => "v1"; }

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TypeScript example AppCatalog keeps construction and access in one place so callers share the same catalog. They obtain instance instead of constructing another catalog. // Own construction so callers do not create separate catalogs. class AppCatalog { static #shared: AppCatalog | undefined; readonly version = "v1"; private constructor() {} // Create on first synchronous access and reuse the object within this module instance. static get instance(): AppCatalog { return AppCatalog.#shared ??= new AppCatalog(); } } const first = AppCatalog.instance; const second = AppCatalog.instance; console.log(first === second); console.log(first.version); true v1 The sharing scope is the same JavaScript module instance. A TypeScript private constructor is a type-checking restriction, not a security boundary against JavaScript callers.

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Each example is a separate .NET 10 console program.

Each C# example is a separate .NET 10 console program. Compile the TypeScript examples for ES2022 or later and run the emitted JavaScript with Node.js.

Singleton Pattern

Body changes between the two selected stored revisions. Code is not executed.

4 changed sections

− Removed+ Added21 unchanged content blocks omitted.

Content blocks 14 → 14

Content blocks 19 → 19

using System; using System.Collections.Generic; using System.Linq; var tasks = Enumerable.Range(0, 8) .Select(_ => System.Threading.Tasks.Task.Run(() => AppCatalog.Instance)).ToArray(); var values = await System.Threading.Tasks.Task.WhenAll(tasks); Console.WriteLine(values.All(value => ReferenceEquals(value, values[0]))); Console.WriteLine(values[0].Version); // Own construction so callers do not create separate catalogs. sealed class AppCatalog { private static readonly Lazy<AppCatalog> shared = new(() => new AppCatalog()); private AppCatalog() { } // Create on first synchronous access and reuse the object within this module instance. public static AppCatalog Instance => shared.Value; public string Version => "v1"; }

Content blocks none → 22-26

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Content blocks 24 → 29-30

Each example is a separate .NET 10 console program.

Each C# example is a separate .NET 10 console program. Compile the TypeScript examples for ES2022 or later and run the emitted JavaScript with Node.js.