c# - 避免非只读静态字段 - Immutability NDepend

Question

我正在使用 NDepend 进行代码分析并收到此警告:

https://www.ndepend.com/default-rules/NDepend-Rules-Explorer.html?ruleid=ND1901# !

此规则对未声明为只读的静态字段发出警告。

在面向对象编程中，保存可修改状态的自然产物是实例字段。此类可变静态字段会在运行时造成对预期状态的混淆，并削弱代码的可测试性，因为每个测试都会重复使用相同的可变状态。

我的代码如下:

using Cosmonaut;
using Microsoft.Azure.Documents.Client;
using System.Configuration;
using LuloWebApi.Entities;


namespace LuloWebApi.Components
{
    /// <summary>
    /// Main class that encapsulates the creation of instances to connecto to Cosmos DB
    /// </summary>
    public sealed class CosmosStoreHolder
    {
        /// <summary>
        /// Property to be initiated only once in the constructor (singleton)
        /// </summary>
        private static CosmosStoreHolder instance = null;

        /// <summary>
        /// To block multiple instance creation
        /// </summary>
        private static readonly object padlock = new object();

        /// <summary>
        /// CosmosStore object  to get tenants information
        /// </summary>
        public Cosmonaut.ICosmosStore<SharepointTenant> CosmosStoreTenant { get; }

        /// <summary>
        /// CosmosStore object  to get site collection information
        /// </summary>
        public Cosmonaut.ICosmosStore<SiteCollection> CosmosStoreSiteCollection { get; }

        /// <summary>
        /// CosmosStore object  to get page templates information
        /// </summary>
        public Cosmonaut.ICosmosStore<PageTemplate> CosmosStorePageTemplate { get; }

        /// <summary>
        /// CosmosStore object  to get pages information
        /// </summary>
        public Cosmonaut.ICosmosStore<Page> CosmosStorePage { get; }

        /// <summary>
        /// CosmosStore object  to get roles information
        /// </summary>
        public Cosmonaut.ICosmosStore<Role> CosmosStoreRole { get; }

        /// <summary>
        /// CosmosStore object  to get clients information
        /// </summary>
        public Cosmonaut.ICosmosStore<Client> CosmosStoreClient { get; }

        /// <summary>
        /// CosmosStore object  to get users information
        /// </summary>
        public Cosmonaut.ICosmosStore<User> CosmosStoreUser { get; }

        /// <summary>
        /// CosmosStore object  to get partners information
        /// </summary>
        public Cosmonaut.ICosmosStore<Partner> CosmosStorePartner { get; }

        /// <summary>
        /// CosmosStore object  to get super administrators information
        /// </summary>
        public Cosmonaut.ICosmosStore<SuperAdministrator> CosmosStoreSuperAdministrator { get; }

        /// <summary>
        /// Constructor
        /// </summary>
        CosmosStoreHolder()
        {

            CosmosStoreSettings settings = new Cosmonaut.CosmosStoreSettings(ConfigurationManager.AppSettings["database"].ToString(),
                 ConfigurationManager.AppSettings["endpoint"].ToString(),
                 ConfigurationManager.AppSettings["authKey"].ToString());

            settings.ConnectionPolicy = new ConnectionPolicy
            {
                ConnectionMode = ConnectionMode.Direct,
                ConnectionProtocol = Protocol.Tcp
            };


            CosmosStoreTenant = new CosmosStore<SharepointTenant>(settings);
            CosmosStoreSiteCollection = new CosmosStore<SiteCollection>(settings);
            CosmosStorePageTemplate = new CosmosStore<PageTemplate>(settings);
            CosmosStorePage = new CosmosStore<Page>(settings);
            CosmosStoreRole = new CosmosStore<Role>(settings);
            CosmosStoreClient = new CosmosStore<Client>(settings);
            CosmosStoreUser = new CosmosStore<User>(settings);
            CosmosStorePartner = new CosmosStore<Partner>(settings);
            CosmosStoreSuperAdministrator = new CosmosStore<SuperAdministrator>(settings);
        }

        /// <summary>
        /// Instance access, singleton
        /// </summary>
        public static CosmosStoreHolder Instance
        {
            get
            {
                lock (padlock)
                {
                    if (instance == null)
                    {
                        instance = new CosmosStoreHolder();
                    }
                    return instance;
                }
            }
        }
    }
}

但是我不确定如何修复此警告。

Answer 1

这是一个指南，不是硬性规定。通常，非只读静态字段很难凭直觉理解。但在这种情况下，您正在执行延迟延迟加载，所以... lock 和 mutate 确实是实现此目的的一种方法，而不会导致它过早加载。

所以一个务实的解决方法是:忽略/覆盖警告

---

然而，另一种方法是将字段移动到另一种类型，它是只读的，并依赖于延迟的 .cctor 语义:

public static CosmosStoreHolder Instance {
   [MethodImpl(MethodImplOptions.NoInlining)]
   get => DeferredHolder.Instance;
}

private static class DeferredHolder {
    internal static readonly CosmosStoreHolder Instance = new CosmosStoreHolder();
}

那么您甚至不需要锁语义(.cctor 会为您处理)。