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duck类型动态对象派生

duck-typing dynamic .net c#

Michael Nero · 技术社区 · 14 年前

我编写了一个类,它允许派生函数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;
        }
    }
}

和派生类:

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,但我在隐式强制转换时会得到runtimebinderException,或者在显式强制转换self-hydrainatingentity返回t时会得到invalidcasteException。

我知道您可以重写dynamicObject.tryconvert方法,但是我想知道什么就是这个方法。我今天读了很多关于duck打字的文章,并尝试了几个库,但没有一个库适用于这个特定的场景。我今天尝试的所有库都使用反射生成了一个包装类。emit调用“get”和“set”方法,并自然地使用反射在包装的实例上找到这些方法。当然,自我保湿没有定义“获取”和“设定”方法。

所以,我想知道这种事情是否可能。有没有办法给T树立一个自我保湿的榜样?我在找这样的东西:

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);

2 回复 | 直到 9 年前

Community Tales Farias 7 年前

你看到这个了吗 Duck Typing 项目。看起来不错。我刚找到一个 great example 从 Mauricio . 它使用windsor castle动态代理拦截方法调用

使用Mauricio的代码,下面的代码就像一个梦

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);
    }
}

jbtule 9 年前

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

无法将接口静态转换为从dynamicObject派生的对象。