C# Lambda 表达式帮助

发布于 2024-08-08 21:59:23 字数 389 浏览 3 评论 0原文

如果我使用如下所示的 lambda 表达式，

// assume sch_id is a property of the entity Schedules
public void GetRecord(int id)
{
    _myentity.Schedules.Where(x => x.sch_id == id));
}

我假设（尽管未经测试）我可以使用匿名内联函数重写它，使用类似

_jve.Schedules.Where(delegate(Models.Schedules x) { return x.sch_id == id; });

我的问题是，我将如何在普通（非内联）函数中重写它，并且还是传入id参数。

原文

If I use a lambda expression like the following

// assume sch_id is a property of the entity Schedules
public void GetRecord(int id)
{
    _myentity.Schedules.Where(x => x.sch_id == id));
}

I'm assuming (although non-tested) I can rewrite that using an anonymous inline function using something like

_jve.Schedules.Where(delegate(Models.Schedules x) { return x.sch_id == id; });

My question is, how would I rewrite that in a normal (non-inline) function and still pass in the id parameter.

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若无相欠,怎会相见 2024-08-15 21:59:23

简而言之，你不能将其作为一个独立的函数。在您的示例中，id实际上保存在闭包中。

长的答案是，您可以编写一个捕获状态的类，方法是使用要操作的 id 值进行初始化，并将其存储为成员变量。在内部，闭包的操作类似 - 区别在于它们实际上捕获对变量的引用而不是它的副本。这意味着闭包可以“看到”它们所绑定的变量的更改。有关详细信息，请参阅上面的链接。

因此，例如：

public class IdSearcher
{
     private int m_Id; // captures the state...
     public IdSearcher( int id ) { m_Id = id; }
     public bool TestForId( in otherID ) { return m_Id == otherID; }
}

// other code somewhere...
public void GetRecord(int id)
{
    var srchr = new IdSearcher( id );
    _myentity.Schedules.Where( srchr.TestForId );
}

The short answer is that you can't make it a stand-along function. In your example, id is actually preserved in a closure.

The long answer, is that you can write a class that captures state by initializing it with the id value you want to operate against, storing it as a member variable. Internally, closures operate similarly - the difference being that they actually capture a reference to the variable not a copy of it. That means that closures can "see" changes to variables they are bound to. See the link above for more details on this.

So, for example:

public class IdSearcher
{
     private int m_Id; // captures the state...
     public IdSearcher( int id ) { m_Id = id; }
     public bool TestForId( in otherID ) { return m_Id == otherID; }
}

// other code somewhere...
public void GetRecord(int id)
{
    var srchr = new IdSearcher( id );
    _myentity.Schedules.Where( srchr.TestForId );
}

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电影里的梦 2024-08-15 21:59:23

如果您只想将委托的主体放在其他地方，您可以使用此实现

public void GetRecord(int id)
{
    _myentity.Schedules.Where(x => MyMethodTooLongToPutInline(x, id));
}
private bool MyMethodTooLongToPutInline(Models.Schedules x, int id)
{
    //...
}

If you only want to place the body of the delegate somewhere else you can achieve using this

public void GetRecord(int id)
{
    _myentity.Schedules.Where(x => MyMethodTooLongToPutInline(x, id));
}
private bool MyMethodTooLongToPutInline(Models.Schedules x, int id)
{
    //...
}

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