How Do Foreach Loops Work in C#, and Which Classes Implement Them?

Understanding C#'s foreach Loops and Their Implementation

Which Classes Employ foreach Loops?

The foreach loop in C# is heavily utilized with classes implementing IEnumerable or IEnumerable<T>. This includes any class providing a GetEnumerator() method that returns an IEnumerator or IEnumerator<T>. Essentially, this covers all classes implementing ICollection or ICollection<T>, such as arrays, lists, and other collections.

foreach Loop Mechanics:

A standard foreach loop (e.g., foreach (int i in obj) { ... }) functionally resembles this:

<code class="language-csharp">var tmp = obj.GetEnumerator();
int i; // C# 4.0 and earlier
while (tmp.MoveNext()) {
    int i; // C# 5.0 and later
    i = tmp.Current;
    { ... } // Loop body
}</code>

Important considerations: If the enumerator (tmp) implements IDisposable, it's disposed of (similar to a using statement). The declaration of int i differs depending on the C# version. In C# 5.0 and later, it's declared inside the loop; earlier versions declare it outside. This distinction is crucial when using i within anonymous methods or lambda expressions inside the loop.

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