迭代强类型泛型List <T>的最佳方法是什么？

在C#.NET和VB.NET中迭代强类型泛型List的最佳方法是什么？

对于C#:

foreach(ObjectType objectItem in objectTypeList)
{
    // ...do some stuff
}

从Purple Ant回答VB.NET :

For Each objectItem as ObjectType in objectTypeList
    'Do some stuff '
Next

对于IEnumerable的任何通用实现,最好的方法是:

//C#
foreach( var item in listVariable) {
    //do stuff
}

但是有一个重要的例外.IEnumerable涉及Current()和MoveNext()的开销,这是foreach循环实际编译成的内容.

当你有一个简单的结构数组:

//C#
int[] valueTypeArray;
for(int i=0; i < valueTypeArray.Length; ++i) {
     int item = valueTypeArray[i];
     //do stuff
}

更快.

更新

在与@Steven Sudit讨论之后(见评论)我认为我的原始建议可能已经过时或有误,所以我进行了一些测试:

// create a list to test with
var theList = Enumerable.Range(0, 100000000).ToList();

// time foreach
var sw = Stopwatch.StartNew();
foreach (var item in theList)
{
    int inLoop = item;
}
Console.WriteLine("list  foreach: " + sw.Elapsed.ToString());

sw.Reset();
sw.Start();

// time for
int cnt = theList.Count;
for (int i = 0; i < cnt; i++)
{
    int inLoop = theList[i];
}
Console.WriteLine("list  for    : " + sw.Elapsed.ToString());

// now run the same tests, but with an array
var theArray = theList.ToArray();

sw.Reset();
sw.Start();

foreach (var item in theArray)
{
    int inLoop = item;
}
Console.WriteLine("array foreach: " + sw.Elapsed.ToString());

sw.Reset();
sw.Start();

// time for
cnt = theArray.Length;
for (int i = 0; i < cnt; i++)
{
    int inLoop = theArray[i];
}
Console.WriteLine("array for    : " + sw.Elapsed.ToString());

Console.ReadKey();

所以,我在发布中运行了所有优化:

list  foreach: 00:00:00.5137506
list  for    : 00:00:00.2417709
array foreach: 00:00:00.1085653
array for    : 00:00:00.0954890

然后调试没有优化:

list  foreach: 00:00:01.1289015
list  for    : 00:00:00.9945345
array foreach: 00:00:00.6405422
array for    : 00:00:00.4913245

所以它看起来相当一致,for比foreach数组更快,而且数组比通用列表更快.

然而,这是100,000,000次迭代,差异大约是最快和最慢方法之间的.4秒.除非你正在进行大规模的性能关​​键循环,否则不值得担心.