Python's `enumerate` in C# 7.

Enumerate.cs

void Main()
{
	var items = new []{ "first", "second", "third" };

	foreach(var (item, index) in Enumerate(items))
	{
		Console.WriteLine($"{item} is index {index}.");
	}
}

public static IEnumerable<(T, int)> Enumerate<T>(IEnumerable<T> enumerable)
{
	var currentIndex = 0;
	
	foreach(var e in enumerable)
	{
		yield return (e, currentIndex);
		
		currentIndex++;
	}
}