给定以下通用方法：
/// <summary>
/// Performs a MoveNext on the IEnumerator 'Enoomerator'.
/// If it hits the end of the enumerable list, it resets to the beginning.
/// </summary>
/// <returns>If False, MoveNext has failed even after resetting,
/// which means there are no entries in the list.</returns>
private static bool CyclicalSafeMoveNext<T>(T Enoomerator)
where T : IEnumerator<T>
{
if (Enoomerator.MoveNext()) // successfully moved to the next element
{
return true;
}
else
{
// Either reached last element (so reset to beginning) or
// trying to enumerate in a list with no entries
LogLine("CyclicalSafeMoveNext: failed a MoveNext, resetting.");
Enoomerator.Reset();
if (!Enoomerator.MoveNext())
{
// Still at end. Zero entries in the list?
LogLine("CyclicalSafeMoveNext: failed a MoveNext after
Reset(), which means there were no entries in the list.");
return false;
}
else
{
// Resetting was successful
return true;
}
}
}
当我编译这段代码
IEnumerator<FileInfo> FileInfoEnumerator files;
while (CyclicalSafeMoveNext(files))
{
return files.Current.FullName;
}
我得到错误：
Error 7 The type 'System.Collections.Generic.IEnumerator<System.IO.FileInfo>' cannot
be used as type parameter 'T' in the generic type or method
'CyclicalSafeMoveNext<T>(T)'. There is no implicit reference conversion from
'System.Collections.Generic.IEnumerator<System.IO.FileInfo>' to 'System.Collections.Generic.IEnumerator<System.Collections.Generic.IEnumerator<System.IO.FileInfo>>'.
为什么会出现此错误，以及如何更正我的代码？
一个问题在这里：
where T : IEnumerator<T>
您将泛型类限制为自己的枚举器类。
由于FileInfo不是IEnumerator<FileInfo>和IEnumerator<FileInfo>不是，IEnumerator<IEnumerator<FileInfo>>它将使通用约束失效。
您可以添加第二个泛型类型：
private static bool CyclicalSafeMoveNext<T, U>(T Enoomerator)
where T : IEnumerator<U>
或只是IEnumerator<T>签名的一部分：
private static bool CyclicalSafeMoveNext<T>(IEnumerator<T> Enoomerator)
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