“不客气".NET 中的实例方法

Some follow-up years later: The incorrectly-bound target that caused func42(CultureInfo.InvariantCulture); to return "-201040128" instead of "42" in my example was memory corruption that could have allowed remote code execution (cve-2010-1898); this was fixed in 2010 in the ms10-060 security update. Current frameworks correctly print 42! That doesn't make answering this question any easier, but explains the particularly weird behavior in the example.

推荐答案

您实际上选择了一个特别棘手的示例，原因有两个:

You've actually chosen a particularly tricky example, for two reasons:

• ToString() 是继承自 object 但在 Int32 中被覆盖的虚方法.
• int 是一个值类型，当涉及到值类型和实例方法时，Delegate.CreateDelegate() 有一些奇怪的规则——基本上第一个有效参数变成了ref int 而不是 int

• ToString() is a virtual method inherited from object but overridden in Int32.
• int is a value type, and there are weird rules with Delegate.CreateDelegate() when it comes to value types and instance methods - basically the first effective parameter becomes ref int rather than int

但是，下面是 String.ToUpper 的示例，它不存在这些问题:

However, here's an example for String.ToUpper, which doesn't have either of those problems:

using System;
using System.Reflection;

class Test
{
    static void Main()
    {
        MethodInfo method = typeof(string).GetMethod
            ("ToUpper", BindingFlags.Instance | BindingFlags.Public,
             null, new Type[]{}, null);

        Func<string, string> func = (Func<string, string>)
            Delegate.CreateDelegate(typeof(Func<string, string>),
                                    null,
                                    method);

        string x = func("hello");

        Console.WriteLine(x);
    }
}

如果这对你来说足够好，那太好了......如果你真的想要 int.ToString，我将不得不更加努力:)

If that's good enough for you, great... if you really want int.ToString, I'll have to try a bit harder :)

这是一个值类型的例子，使用一个新的委托类型，它通过引用获取它的第一个参数:

Here's an example for a value type, using a new delegate type which takes its first parameter by reference:

using System;
using System.Reflection;

public struct Foo
{
    readonly string value;

    public Foo(string value)
    {
        this.value = value;
    }

    public string DemoMethod()
    {
        return value;
    }
}

class Test
{
    delegate TResult RefFunc<TArg, TResult>(ref TArg arg);

    static void Main()
    {
        MethodInfo method = typeof(Foo).GetMethod
            ("DemoMethod", BindingFlags.Instance | BindingFlags.Public,
             null, new Type[]{}, null);
        RefFunc<Foo, string> func = (RefFunc<Foo, string>)
            Delegate.CreateDelegate(typeof(RefFunc<Foo, string>),
                                    null,
                                    method);

        Foo y = new Foo("hello");
        string x = func(ref y);

        Console.WriteLine(x);
    }
}

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