使用Linq生成要从另一个集合中删除的内容集合

我很熟悉在使用 foreach

之前的代码,该代码引发了异常:

IEnumerable<Guid> keysToDelete = _outConnections.Where(
    pair => pair.Value < timeoutPoint
).Select(pair => pair.Key);

foreach (Guid key in keysToDelete)
{
    ...some stuff not dealing with keysToDelete...
    _outConnections.Remove(key);
}

List<Guid> keysToDelete = _outConnections.Where(
    pair => pair.Value < timeoutPoint
).Select(pair => pair.Key).ToList();

for (int i=keysToDelete.Count-1; i>=0; i--)
{
    Guid key = keysToDelete[i];
    ...some stuff not dealing with keysToDelete...
    _outConnections.Remove(key);
}

为什么会这样?我有一种感觉,可能我的Linq查询并没有真正返回新集合,而是返回原始集合的某个子集,因此它指责我修改集合 keysToDelete 当我从中删除一个元素时 _outConnections .

更新:

List<Guid> keysToDelete = _outConnections.Where(
    pair => pair.Value < timeoutPoint
).Select(pair => pair.Key).ToList();

foreach (Guid key in keysToDelete)
{
    ...some stuff not dealing with keysToDelete...
    _outConnections.Remove(key);
}