foreach and IEnumerator

[George2]

Hello everyone,


Two questions,

1.

How foreach utilizes the IEnumerator interface and IEnumerable interface? Any there any docuements? I am interested in it.

2.

Pros and cons compared with using foreach and using simple index variable to iterate? Like,


for (int i = 0; i < abc.Count; i++)
{
// access abc [i] here
}



thanks in advance,
George

[Magos]

1)
"foreach" is just syntactic sugar for:

IEnumerable c; //Some enumerable container
IEnumerator e = c.GetEnumerator(); //Get enumerator to first element

while(e.MoveNext()) //Loop while there are more elements
{
e.Current; //Do something with current element
}


2)
foreach can be used on any enumerable, not just those who can be indexed.
As for differences in efficinecy I'm sure it depends from case to case.

[George2]

Thanks Magos,


I have found some code, share here.

http://www.csharpfriends.com/Spec/index.aspx?specID=15.8.4.htm

I read the document. There are two expansions for foreach, but I can not distinguish the differences, what are the differences?

--------------------
2 If the collection expression is of a type that implements the collection pattern (as defined above), the expansion of the foreach statement is:

3 Otherwise; the collection expression is of a type that implements System.IEnumerable, and the expansion of the foreach statement is:
--------------------

1)
"foreach" is just syntactic sugar for:

IEnumerable c; //Some enumerable container
IEnumerator e = c.GetEnumerator(); //Get enumerator to first element

while(e.MoveNext()) //Loop while there are more elements
{
e.Current; //Do something with current element
}


2)
foreach can be used on any enumerable, not just those who can be indexed.
As for differences in efficinecy I'm sure it depends from case to case.


regards,
George