C＃防爆pression树木和调用一个委托 [英] C# Expression Trees and Invoking a Delegate

问题描述

所以我有一个代理其中指出了一些功能，我真的不知道当我第一次创建代理对象。的对象被设置为一些功能以后

So I have a delegate which points to some function which I don't actually know about when I first create the delegate object. The object is set to some function later.

我也那么想打一个前pression树调用委托有一个参数（对于这个问题的缘故参数可以是 5 ）。这是位我挣扎;在code以下显示了我想要的，但它并没有编译。

I also then want to make an expression tree that invokes the delegate with an argument (for this question's sake the argument can be 5). This is the bit I'm struggling with; the code below shows what I want but it doesn't compile.

Func<int, int> func = null;
Expression expr = Expression.Invoke(func, Expression.Constant(5));

在这个例子中，我可以做的（这是可行的，因为我需要建立前pression树木在运行时）：

For this example I could do (this is practical since I need to build the expression trees at runtime):

Func<int, int> func = null;
Expression<Func<int>> expr = () => func(5);

这使得 EXPR 成为：

() => Invoke(value(Test.Program+<>c__DisplayClass0).func, 5)

这似乎意味着，使用代理 FUNC ，我需要制作的值（Test.Program +＆LT;＆GT; c__DisplayClass0）。.FUNC 位

Which seems to mean that to use the delegate func, I need to produce the value(Test.Program+<>c__DisplayClass0).func bit.

那么，如何才能让一个前pression树，调用一个代表？

So, how can I make an expression tree which invokes a delegate?

推荐答案

确定，这说明它是如何的可以的完成（但它是非常不雅的在我看来）：

OK, this shows how it can be done (but it is very inelegant in my opinion):

Func<int, int> func = null;
Expression<Func<int, int>> bind = (x) => func(x);

Expression expr = Expression.Invoke(bind, Expression.Constant(5));

Expression<Func<int>> lambda = Expression.Lambda<Func<int>>(expr);
Func<int> compiled = lambda.Compile();

Console.WriteLine(expr);

func = x => 3 * x;
Console.WriteLine(compiled());

func = x => 7 * x;
Console.WriteLine(compiled());

Console.Read();

基本上我用（X）=＆GT; FUNC（X）; 来使一个函数调用什么委托点。但是你可以看到， EXPR 是过于复杂。出于这个原因，我不认为这个答案不错，但也许它可以在建？

Essentially I use (x) => func(x); to make a function that calls what the delegate points to. But you can see that expr is overly complicated. For this reason I don't consider this answer good, but maybe it can be built upon?

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