Duck Typing DynamicObject衍生

Question

我写了一个类，允许派生指定哪些属性可以延迟加载。该代码是：

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; 
     } 
    } 
} 

而一个衍生类：

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)); 
    } 
} 

这工作完全正常获取和设置属性值，但我得到一个既可以当我隐式转换一个RuntimeBinderException或与一个InvalidCastException明确地将SelfHydratingEntity转换回T.

我知道你可以覆盖DynamicObject.TryConvert方法，但是我想知道究竟是什么这个方法。我今天读了很多关于鸭子打字的文章，并尝试了几个图书馆，但没有一个适用于这种特殊情况。我今天尝试过的所有库都使用Reflection.Emit生成一个包装类，它调用“get_”和“set_”方法，并自然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。有什么办法将SelfHydratingEntity的实例投射到T？我正在寻找这样的事情：

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

你见过这个Duck Typing项目。它看起来不错。我刚刚从Mauricio找到great example。它采用了温莎城堡动态代理拦截方法调用

使用从毛下面的代码工作就像一个梦

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

即兴接口代码 https://github.com/ekonbenefits/impromptu-interface

可以静态浇铸接口上派生的对象来自DynamicObject。