What Types of C# Classes Support Foreach Loops?

foreach loop in C#

Question:

What types of classes allow the use of foreach loops?

Answer:

Technically, any class that has a public method named GetEnumerator() that returns a type with a bool MoveNext() method and a Current property can be used. However, the most common explanation involves a class that implements IEnumerable or IEnumerable, returning an IEnumerator or IEnumerator.

By extension, any class that implements ICollection or ICollection (e.g., Collection, List, Array (T[])) can support foreach loops.

How it works:

The foreach loop works as follows:

• Initialize a temporary object (tmp) from the GetEnumerator() method of the given object (obj).
• As long as tmp.MoveNext() returns true, the loop body (surrounded by {...}) is executed repeatedly, containing the current value of Current.

Variations:

• If tmp supports IDisposable, use it to dispose of tmp when the loop completes.
• C# 5.0 allows variables like i to be declared inside a loop, whereas in earlier versions they had to be declared outside the loop. This distinction becomes critical when using i in an anonymous method or lambda expression inside a loop.

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