Csharp 为什么in关键字允许 C# 属性发生变化

发布于07月24日

我目前正在处理一个函数，其中传递了一个对象(自写类型Catalog)，并且不会在被调用的函数中进行Mutations /更改.这里有一个简单的例子.


public override bool Migrate(in Catalog fromCatalog)
{
    fromCatalog.SupplierId = 1; //works, but why
}

我想要严格 destruct 这种行为和disallow mutating any properties个传递的对象.

推荐答案

因为in修饰符仅适用于变量(本例中的参数).它可以防止将参数值更改为引用不同的对象.

public bool Migrate(in Catalog fromCatalog)
{
/* Error CS8331  Cannot assign to variable 'fromCatalog' 
or use it as the right hand side of a ref assignment 
because it is a readonly variable */
    fromCatalog = new Catalog(); 

    fromCatalog.SupplierId = 1;
}

并创建对象的浅表副本，这样您就不会更改传递的对象中的任何内容(在类中)

example:个

public Catalog CreateACopy()
{
    Catalog obj = (Catalog)this.MemberwiseClone();
    // and other...
    return obj;
}

utilization:

public class Program 
{
    private static void Main()
    {
        Catalog catalog = new Catalog();
        new Program().Migrate(catalog.CreateACopy());
    }
    public bool Migrate(in Catalog fromCatalog)
    {
        fromCatalog.SupplierId = 1;
    }
}