Cool new way to fill array with a value in .NET Core

Can you count how many times you wrote something like:

var prime = new bool[1000];
for ( int i = 0; i < isPrime.Length; i++ )
prime[i] = true;

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Or if you fancy LINQ (and can sacrifice a bit of performance)?

var prime = Enumerable.Repeat(true, 1000).ToArray();

If your answer is infinite or more, then check out the new way available in .NET Core 2.0 and newer:

var data = new bool[1000];
Array.Fill(data, true);

Array.Fill brings the best of both worlds – it is more succinct than a for-loop while being more performant than Enumerable.Repeat.

As .NET Core is open source and we like to peek under the hood, we can see the Array.Fill method is basically just a shorthand for plain for loop:

public static void Fill<T>(T[] array, T value)
if (array == null)
for (int i = 0; i < array.Length; i++)
array[i] = value;

It is also worth mentioning that Array.Fill has another overload which lets us specify which range of indices should be filled:

public static void Fill<T> (T[] array, T value, int startIndex, int count);

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