Duck Typing DynamicObject 派生

Question

我编写了一个类，它允许派生指定哪些属性可以延迟加载。代码是：

public abstract class SelfHydratingEntity<T> : DynamicObject where T : class {
    private readonly Dictionary<string, LoadableBackingField> fields;

    public SelfHydratingEntity(T original) {
        this.Original = original;
        this.fields = this.GetBackingFields().ToDictionary(f => f.Name);
    }

    public T Original { get; private set; }

    protected virtual IEnumerable<LoadableBackingField> GetBackingFields() {
        yield break;
    }

    public override bool TryGetMember(GetMemberBinder binder, out object result) {
        LoadableBackingField field;
        if (this.fields.TryGetValue(binder.Name, out field)) {
            result = field.GetValue();
            return true;
        } else {
            var getter = PropertyAccessor.GetGetter(this.Original.GetType(), binder.Name);
            result = getter(this.Original);
            return true;
        }
    }

    public override bool TrySetMember(SetMemberBinder binder, object value) {
        LoadableBackingField field;
        if (this.fields.TryGetValue(binder.Name, out field)) {
            field.SetValue(value);
            return true;
        } else {
            var setter = PropertyAccessor.GetSetter(this.Original.GetType(), binder.Name);
            setter(this.Original, value);
            return true;
        }
    }
}

还有一个派生类：

public class SelfHydratingPerson : SelfHydratingEntity<IPerson> {
    private readonly IDataRepository dataRepository;

    public SelfHydratingDerivate(IDataRepository dataRepository, IPerson person)
        : base(person) {
        this.dataRepository = dataRepository
    }

    protected override IEnumerable<LoadableBackingField> GetBackingFields() {
        yield return new LoadableBackingField("Address", () => this.dataRepository.Addresses.Get(this.Original.AddressID));
    }
}

这对于获取和设置属性值非常有效，但是当我隐式强制转换时我会得到一个 RuntimeBinderException 或者一个 InvalidCastException 并且将 SelfHydratingEntity 显式强制转换回 T。

我知道您可以重写 DynamicObject.TryConvert 方法，但我想知道 什么 到底要放入这个方法。我今天读了很多关于鸭子类型的文章，并尝试了几个库，但它们都不适用于这种特殊情况。我今天尝试的所有库都使用 Reflection.Emit 生成一个包装器类，该类调用“get_”和“set_”方法，并自然地使用反射在包装实例上查找这些方法。 SelfHydratingEntity 当然没有定义“get_”和“set_”方法。

所以，我想知道这种事情是否可能。有没有办法将 SelfHydratingEntity 的实例转换为 T？我正在寻找这样的东西：

var original = GetOriginalPerson();
dynamic person = new SelfHydratingPerson(new DataRepository(), original);

string name = person.Name;    // Gets property value on original
var address = person.Address; // Gets property value using LoadableBackingField registration

var iPerson = (IPerson)person;
- or -
var iPerson = DuckType.As<IPerson>(person);

Answer 1

你看过这个Duck Typing 项目吗？它看起来很不错。我刚刚从Mauricio 中找到了great example。它使用温莎城堡动态代理来拦截方法调用

使用 Mauricio 的代码，下面的代码就像梦一样工作

class Program
{
    static void Main(string[] args)
    {
        dynamic person = new { Name = "Peter" };
        var p = DuckType.As<IPerson>(person);

        Console.WriteLine(p.Name);
    }
}

public interface IPerson
{
    string Name { get; set; }
}

public static class DuckType
{
    private static readonly ProxyGenerator generator = new ProxyGenerator();

    public static T As<T>(object o)
    {
        return generator.CreateInterfaceProxyWithoutTarget<T>(new DuckTypingInterceptor(o));
    }
}

public class DuckTypingInterceptor : IInterceptor
{
    private readonly object target;

    public DuckTypingInterceptor(object target)
    {
        this.target = target;
    }

    public void Intercept(IInvocation invocation)
    {
        var methods = target.GetType().GetMethods()
            .Where(m => m.Name == invocation.Method.Name)
            .Where(m => m.GetParameters().Length == invocation.Arguments.Length)
            .ToList();
        if (methods.Count > 1)
            throw new ApplicationException(string.Format("Ambiguous method match for '{0}'", invocation.Method.Name));
        if (methods.Count == 0)
            throw new ApplicationException(string.Format("No method '{0}' found", invocation.Method.Name));
        var method = methods[0];
        if (invocation.GenericArguments != null && invocation.GenericArguments.Length > 0)
            method = method.MakeGenericMethod(invocation.GenericArguments);
        invocation.ReturnValue = method.Invoke(target, invocation.Arguments);
    }
}

Answer 2

即兴界面 https://github.com/ekonbenefits/impromptu-interface

可以将接口静态转换为从 DynamicObject 派生的对象。