在 Matlab 中迭代 C# 迭代器（IEnumerable）

Question

我有一个返回大量对象的 C# 方法。这是要在 Matlab 中使用的。

namespace MyNameSpace{
    public static class MyClass{
        public static IEnumerable<MyDataObject> GetVeryLargeResponse(){
            while(CheckForSomeFunkyConditionThatsRarelyTrue()){
               yield return GetMyNextDataObject();
            }
            yield break;
        }
    }
}

我打电话时在 Matlab 中

result = MyClass.GetVeryLargeResponse();

我希望结果是IEnumerable<MyDataObject> 类型，以便能够通过调用result.GetEnumerator() 获得Enumerator<MyDataObject>。

当我得到result 时，它是MyNameSpace.<GetVeryLargeResponse>d_3 类型，没有可用的GetEnumerator() 方法。我确实看到result 的超级类之一是System.Collections.Generic.IEnumerable<MyClass>。

有没有一种方法可以在 Matlab 中进行迭代，甚至可以在 Matlab 中将result“转换”为IEnumerable<MyClass>。

附言

1. 由于数据量大，无法转换为Array / IList 等
2. 这不是How can I iterate over a C# IEnumerable in Matlab? 的重复，因为它专门处理IQueryable。
3. 我正在使用 Matlab 2010b

Answer 1

结果确实有一个GetEnumerator() 方法——它只是可以通过显式接口实现来实现。

如果 Matlab 不愿意处理，您可以随时编写自己的映射类型和扩展方法以使事情变得更简单：

public static class Extensions
{
    public static EnumerableWrapper<T> Wrap<T>(this IEnumerable<T> source)
    {
        return new EnumerableWrapper<T>(source);
    }
}

public class EnumerableWrapper<T> : IEnumerable<T>
{
    private readonly IEnumerable<T> source;

    public EnumerableWrapper(IEnumerable<T> source)
    {
        this.source = source;
    }

    public IEnumerator<T> GetEnumerator()
    {
        return new EnumeratorWrapper<T>(source.GetEnumerator());
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}

public class EnumeratorWrapper<T> : IEnumerator<T>
{
    private readonly IEnumerator<T> source;

    public EnumeratorWrapper(IEnumerator<T> source)
    {
        this.source = source;
    }

    public T Current { get { return source.Current; } }

    object IEnumerator.Current { get { return Current; } }

    public bool MoveNext()
    {
        return source.MoveNext();
    }

    public void Reset()
    {
        source.Reset();
    }

    public void Dispose()
    {
        source.Dispose();
    }

}

那就试试吧：

result = MyClass.GetVeryLargeResponse().Wrap();

虽然 Matlab 不那么支持开箱即用，这似乎很奇怪......

Answer 2

考虑以下示例：

MyClass.cs

namespace MyNameSpace {
    public class Person {
        public string name { get; set; }
        public int age { get; set; }
    }

    public class MyClass {
        private static List<Person> people = new List<Person> {
            new Person {name = "name1", age=10},
            new Person {name = "name2", age=20},
            new Person {name = "name3", age=30},
            new Person {name = "name4", age=40},
            new Person {name = "name5", age=50}
        };

        public static IEnumerable<Person> GetPeople() {
            foreach (var p in people) {
                yield return p;
            }
        }
    }
}

code.m

%# load my assembly
str = 'C:\path\to\MyNameSpace.dll';
NET.addAssembly(str);

obj = MyNameSpace.MyClass.GetPeople();   %# IEnumerable<Person>

%# call ToArray() extension method: this forces immediate query evaluation
NET.addAssembly('System.Core');          %# contains 'System.Linq' namespace
arr = NET.invokeGenericMethod('System.Linq.Enumerable', 'ToArray', ...
    {'MyNameSpace.Person'}, obj);

%# loop through results
for i=1:arr.Length
    fprintf('name=%s, age=%d\n', char(arr(i).name), int32(arr(i).age));
end

代码产生输出：

name=name1, age=10
name=name2, age=20
name=name3, age=30
name=name4, age=40
name=name5, age=50

如您所见，我确实将返回的对象转换为数组Person[]（我意识到您试图避免这种情况）。奇怪的是，如果我们查看类的层次结构：

>> superclasses(obj)
Superclasses for class MyNameSpace.<GetPeople>d__0:
    System.Object
    System.Collections.Generic.IEnumerable<MyNameSpace*Person>
    System.Collections.IEnumerable
    System.Collections.Generic.IEnumerator<MyNameSpace*Person>
    System.IDisposable
    System.Collections.IEnumerator
    handle

您可以看到System.Collections.Generic.IEnumerator<Person>，但不知何故，该对象似乎没有公开继承的GetEnumerator 方法：

>> methods(obj,'-full')

Methods for class MyNameSpace.<GetPeople>d__0:

MyNameSpace.<GetPeople>d__0 obj <GetPeople>d__0(int32 scalar <>1__state)
logical scalar RetVal Equals(MyNameSpace.<GetPeople>d__0 this, System.Object obj)
int32 scalar RetVal GetHashCode(MyNameSpace.<GetPeople>d__0 this)
System.Type RetVal GetType(MyNameSpace.<GetPeople>d__0 this)
System.String RetVal ToString(MyNameSpace.<GetPeople>d__0 this)
event.listener L addlistener(handle sources, char vector eventname, function_handle scalar callback)  % Inherited from handle
event.proplistener L addlistener(handle sources, meta.property properties, char vector eventname, function_handle scalar callback)  % Inherited from handle
event.proplistener L addlistener(handle sources, string propertyname, char vector eventname, function_handle scalar callback)  % Inherited from handle
event.proplistener L addlistener(handle sources, cell propertynames, char vector eventname, function_handle scalar callback)  % Inherited from handle
delete(handle obj)  % Inherited from handle
logical TF eq(A, B)  % Inherited from handle
handle HM findobj(handle H, varargin)  % Inherited from handle
meta.property prop findprop(handle scalar object, string propname)  % Inherited from handle
logical TF ge(A, B)  % Inherited from handle
logical TF gt(A, B)  % Inherited from handle
logical validity isvalid(handle obj)  % Inherited from handle
logical TF le(A, B)  % Inherited from handle
logical TF lt(A, B)  % Inherited from handle
logical TF ne(A, B)  % Inherited from handle
notify(handle sources, string eventname)  % Inherited from handle
notify(handle sources, string eventname, event.EventData scalar eventdata)  % Inherited from handle

Answer 3

您需要使用显式强制转换。首先显式转换 IEnumerable 实例：

result = MyClass.GetVeryLargeResponse();
resultEnumerable = NET.explicitCast(result,'System.Collections.IEnumerable');

然后获取枚举器：

resultEnumerator = resultEnumerable.GetEnumerator();

然后显式地转换枚举数：

resultEnumerator = NET.explicitCast(resultEnumerator, 'System.Collections.IEnumerator');

然后您可以根据需要遍历集合：

while (resultEnumerator.MoveNext)
    resultEnumerator.Current
end