了解F＃3.0中对受保护/基本成员使用的更改

问题描述

F＃3.0为对 base 和 protected 成员的调用添加了更严格的检查。我有一些像C＃中的抽象类，它有 protected static 辅助方法供派生类使用。

F# 3.0 adds stricter checks for calls to base and protected members. I have something like the following abstract class in C# that has protected static helper methods to be used by derived classes.

public abstract class Processor {
    public abstract void Process();
    protected static void Helper(object arg) { }
}

，其中一个辅助方法作为第一类函数传递：

In F#, one of those helper methods is passed as a first-class function:

type DerivedProcessor() =
  inherit Processor()

  let init f =
    f ()

  override x.Process() =
    init Processor.Helper

它在2.0中编译无投诉，但在3.0中会产生错误：

It compiles without complaint in 2.0, but in 3.0 produces an error:

好，在另一个静态成员中包装调用

OK, it's easy enough to comply, just wrap the call in another static member

static member private HelperWrapper(arg) = Processor.Helper(arg)

并传递该intead。但为什么？

and pass that intead. But why?

C＃对这个模式没有问题。

C# has no problem with this same pattern.

public class HappyToCompile : Processor {
    private void Init(Action<object> f) {
        f(null);
    }

    public override void Process() {
        Init(Helper);
    }
}

问题： / p>

The questions:

1. 为什么要添加更严格的支票？

推荐答案

使用我的心理语言设计技巧，我猜想F＃2.0生成的是不可验证的代码。请参见发表在Eric Lippert的博客上，以解释C＃中的相关问题（自C＃4，IIRC后已修复）。

Using my psychic language design skills, I'd guess that F# 2.0 is generating unverifiable code. See this post on Eric Lippert's blog for an explanation of a related issue in C# (which has been fixed since C# 4, IIRC).

总之，创建一个F＃函数，你真正创建一个新类派生自 FSharpFunc ，并从该类中调用您的protected方法是无效的，因为它不在

In short, when you create an F# function you are really creating a new class deriving from FSharpFunc<_,_>, and calling your protected method from within that class isn't valid since it's not in the inheritance chain.

当然，不是不允许这些调用，编译器可以做你正在做的事情（创建一个私有方法并使用它），但也许这些好处被认为不会超过实施改进的成本。

Of course, rather than disallowing these calls, the compiler could just do what you're doing (create a private method and use that), but perhaps the benefits were thought not to outweigh the cost of implementing that improvement.

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