为什么我不能用 linq 迭代可以用 foreach 迭代的东西？

Question

I have a collection of table rows (type DataRowCollection ). It is perfectly valid for me to write:

foreach(var row in myDataRowCollection)
{
  // Something with row
}

Yet the following will not compile:

myDataRowCollection.ToList();

or even

myDataRowCollection.Select(...

What are these System.Linq extensions expecting that DataRowCollection doesn't implement?

Answer 1

foreach() is pattern based ( docs ), it does not actually rely on IEnumerable . GetEnumerator() is enough.

class A // note: no interface
{
    public IEnumerator GetEnumerator() { ...} 
}

Linq on the other hand is based on extension methods for IEnumerable<T> .

Your DataRowCollection implements IEnumerable but not IEnumerable<DataRow> . It is too old for Linq.

But there are some helper methods available, myDataRowCollection.AsEnumerable().Select(...) should work.