IEnumerable的多个枚举数

您的 EnumerateAs() IEnumerable<T> ,其中T是集合中包含的对象的类型。我建议多读一些关于 yield return

从您的问题中不清楚枚举策略将如何与您的collection类交互。看起来你可能在追求这样的东西:

public interface IEnumerationStrategy<TCollection, T>
{
    IEnumerable<T> Enumerate(TCollection source);
}

public class Quark {}

public class MyCollection
{
    public IEnumerable<Quark> EnumerateAs(IEnumerationStrategy<MyCollection, Quark> strategy)
    {
        return strategy.Enumerate(this);
    }

    //Various special methods needed to implement stategies go here
}

public class SpecialStrategy : IEnumerationStrategy<MyCollection, Quark>
{
    public IEnumerable<Quark> Enumerate(MyCollection source)
    {
        //Use special methods to do custom enumeration via yield return that depends on specifics of MyCollection
    }
}

请注意,还可以用简单的策略替换strategy类 Func<MyCollection, IEnumerable<T>> ,但上面的语法与所需的语法最为匹配。

我建议您首先创建函数GetEnumeratorInFirstStyle、GetEnumeratorInSecondStyle等(当然,要使用适合您的应用程序的名称),然后创建新的结构,例如(vb语法中的示例,但应该很容易转换为C#):

Class enumTest
    Function GetEnumeratorInFirstStyle() As IEnumerator(Of Integer)
        Return Enumerable.Empty(Of Integer)() ' Real code would do something better
    End Function
    Private Structure FirstStyleEnumerable
        Implements IEnumerable(Of Integer)

        Private myEnumTest As enumTest

        Public Function GetEnumerator() As System.Collections.Generic.IEnumerator(Of Integer) Implements System.Collections.Generic.IEnumerable(Of Integer).GetEnumerator
            Return myEnumTest.GetEnumeratorInFirstStyle
        End Function

        Public Function GetEnumerator1() As System.Collections.IEnumerator Implements System.Collections.IEnumerable.GetEnumerator
            Return myEnumTest.GetEnumeratorInFirstStyle
        End Function

        Sub New(ByVal newEnumTest As enumTest)
            myEnumTest = newEnumTest
        End Sub
    End Structure
    Public ReadOnly Property AsFirstStyleEnumerable As IEnumerable(Of Integer)
        Get
            Return New FirstStyleEnumerable(Me)
        End Get
    End Property
End Class

请注意,使用的是结构而不是类,因为使用类需要创建一个新的堆对象并为其访问添加额外的间接级别;该结构的真正目的是允许它实现与封装对象“不同”的IEnumerable<T>。顺便说一句,可以将泛型与标记类一起使用,以避免为枚举的每个变体手动定义新的FirstStyleEnumerator结构。不过,我不确定这是更干净还是更混乱。

Interface IQualifiedEnumerable(Of T, U)
    Function GetEnumerator() As IEnumerable(Of U)
End Interface

Structure QualifiedEnumerableWrapper(Of T, U)
    Implements IEnumerable(Of U)
    Private myEnumerable As IQualifiedEnumerable(Of T, U)

    Public Function GetEnumerator() As System.Collections.Generic.IEnumerator(Of U) Implements System.Collections.Generic.IEnumerable(Of U).GetEnumerator
        Return myEnumerable.GetEnumerator
    End Function

    Public Function GetEnumerator1() As System.Collections.IEnumerator Implements System.Collections.IEnumerable.GetEnumerator
        Return myEnumerable.GetEnumerator
    End Function

    Sub New(ByVal newEnumerable As IQualifiedEnumerable(Of T, U))
        myEnumerable = newEnumerable
    End Sub
End Structure

Class EnumTest2
    Implements IQualifiedEnumerable(Of FirstEnumerationStyle, Integer)
    Implements IQualifiedEnumerable(Of SecondEnumerationStyle, Integer)

    Private Class FirstEnumerationStyle     ' Marker classes for generics
    End Class
    Private Class SecondEnumerationStyle
    End Class

    Private Function GetFirstStyleEnumerator() As System.Collections.Generic.IEnumerable(Of Integer) Implements IQualifiedEnumerable(Of FirstEnumerationStyle, Integer).GetEnumerator
        Return Enumerable.Empty(Of Integer)()
    End Function

    Private Function GetSecondStyleEnumerator() As System.Collections.Generic.IEnumerable(Of Integer) Implements IQualifiedEnumerable(Of SecondEnumerationStyle, Integer).GetEnumerator
        Return Enumerable.Empty(Of Integer)()
    End Function

    Public ReadOnly Property AsFirstStyleEnumerable As IEnumerable(Of Integer)
        Get
            Return New QualifiedEnumerableWrapper(Of FirstEnumerationStyle, Integer)
        End Get
    End Property

    Public ReadOnly Property AsSecondStyleEnumerable As IEnumerable(Of Integer)
        Get
            Return New QualifiedEnumerableWrapper(Of SecondEnumerationStyle, Integer)
        End Get
    End Property
End Class

在这里,接口和结构的定义完全是通用的;向类中添加每个额外的枚举方法需要添加一个函数来返回其枚举数,并添加一个属性来返回适当类型的qualifiedEnumerableRapper。

public class AltEnumerator : System.Collections.IEnumerable
{

    private System.Collections.IEnumerator _base;

    public AltEnumerator(System.Collections.IEnumerator _pbase)
    {
        _base = _pbase;
    }


    #region IEnumerable Members

    public System.Collections.IEnumerator GetEnumerator()
    {
        return _base ;
    }

    #endregion
}

在课堂上,你可以:

    public AltEnumerator Iterate(IterDIrection How )
    {
        switch (How)
        {
            case TwoDimArray<T>.IterDIrection.RghtLeftTopBottom:
                return new AltEnumerator(GetRightLeft());
        }
        return new AltEnumerator(GetEnumerator());
    }

    private System.Collections.IEnumerator GetRightLeft()
    {
        for (int cndx = PutSlotArray.GetLength(1) - 1; cndx >= 0; cndx--)
            for (int rndx = 0; rndx < PutSlotArray.GetLength(0); rndx++)
                if (PutSlotArray[rndx, cndx] != null)
                    yield return PutSlotArray[rndx, cndx];
    }

    #region IEnumerable Members

    public System.Collections.IEnumerator GetEnumerator()
    {
        foreach (T ps in PutSlotArray)
            if (ps != null)
                yield return ps;
    }

    #endregion