C#中的延迟执行 [英] Deferred execution in C#

问题描述

如何在C#中实现自己的延迟执行机制?

How could I implement my own deferred execution mechanism in C#?

例如，我有:

string x = DoFoo();

是否可以执行一些魔术操作，以使DoFoo在我使用" x之前不执行?

Is it possible to perform some magic so that DoFoo does not execute until I "use" x?

推荐答案

您可以使用lambda/delegates:

You can use lambdas/delegates:

Func<string> doit = () => DoFoo();
//  - or -
Func<string> doit = DoFoo;

稍后，您可以像调用方法一样调用doit:

Later you can invoke doit just like a method:

string x = doit();

---

我认为您可以获得的最接近的东西是这样的:

---

I think the closest you can get is something like this:

Lazy<string> x = DoFoo;

string y = x; // "use" x

定义为Lazy<T>与此类似(未经测试):

With a definition of Lazy<T> similar to this (untested):

public class Lazy<T>
{
    private readonly Func<T> func;
    private bool hasValue;
    private T value;

    public Lazy(Func<T> func)
    {
        this.func = func;
        this.hasValue = false;
    }

    public static implicit operator Lazy<T>(Func<T> func)
    {
        return new Lazy<T>(func);
    }

    public static implicit operator T(Lazy<T> lazy)
    {
        if (!lazy.hasValue)
        {
            lazy.value = lazy.func();
            lazy.hasValue = true;
        }
        return lazy.value;
    }
}

不幸的是，似乎编译器的类型推断算法无法自动推断Func<T>的类型，因此无法将其与隐式转换运算符匹配.我们需要显式声明委托的类型，这使赋值语句更加冗长:

Unfortunately, it seems that the compiler's type inferencing algorithms can't auto-infer the type of the Func<T> and so can't match it to the implicit conversion operator. We need to explicitly declare the delegate's type, which makes the assignment statements more verbose:

// none of these will compile...
Lazy<string> x = DoFoo;
Lazy<string> y = () => DoFoo();
Lazy<string> z = delegate() { return DoFoo(); };

// these all work...
Lazy<string> a = (Func<string>)DoFoo;
Lazy<string> b = (Func<string>)(() => DoFoo());
Lazy<string> c = new Func<string>(DoFoo);
Lazy<string> d = new Func<string>(() => DoFoo());
Lazy<string> e = new Lazy<string>(DoFoo);
Lazy<string> f = new Lazy<string>(() => DoFoo);

这篇关于C#中的延迟执行的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！