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    <p>There are two obvious approaches: use <code>Array.Copy</code> and copy elements one by one:</p> <pre><code>private static void ElementByElement&lt;T&gt;(T[] arg, int start) { for (int i = arg.Length - 1; i &gt; start; i--) { arg[i] = arg[i - 1]; } } private static T BuiltInCopy&lt;T&gt;(T[] arg, int start) { Array.Copy(arg, start, arg, start + 1, arg.Length - start - 1); return arg[0]; } </code></pre> <p>On one hand, <code>List&lt;T&gt;</code> insert uses <code>Array.Copy</code>. On the other, <code>Array.Copy</code> is non-generic and can do a <em>lot</em> of extra work: <a href="http://msdn.microsoft.com/en-us/library/z50k9bft.aspx" rel="nofollow noreferrer">http://msdn.microsoft.com/en-us/library/z50k9bft.aspx</a></p> <p>I expected <code>Array.Copy</code> to be faster. However, the results of this MiniBench test surprised me.</p> <pre><code>internal class Program { private static int smallArraySize = 32; public static void Main(string[] args) { BenchArrayCopy(); } private static void BenchArrayCopy() { var smallArrayInt = new int[smallArraySize]; for (int i = 0; i &lt; smallArraySize; i++) smallArrayInt[i] = i; var smallArrayString = new string[smallArraySize]; for (int i = 0; i &lt; smallArraySize; i++) smallArrayString[i] = i.ToString(); var smallArrayDateTime = new DateTime[smallArraySize]; for (int i = 0; i &lt; smallArraySize; i++) smallArrayDateTime[i] = DateTime.Now; var moveInt = new TestSuite&lt;int[], int&gt;("Move part of array right by 1: int") .Plus(BuiltInCopy, "Array.Copy()") .Plus(ElementByElement, "Element by element in a for loop") .RunTests(smallArrayInt, 0); var moveString = new TestSuite&lt;string[], string&gt;("Move part of array right by 1: string") .Plus(BuiltInCopy, "Array.Copy()") .Plus(ElementByElement, "Element by element in a for loop") .RunTests(smallArrayString, "0"); var moveDT = new TestSuite&lt;DateTime[], DateTime&gt;("Move part of array right by 1: DateTime") .Plus(BuiltInCopy, "Array.Copy()") .Plus(ElementByElement, "Element by element in a for loop") .RunTests(smallArrayDateTime, smallArrayDateTime[0]); moveInt.Display(ResultColumns.All, moveInt.FindBest()); moveString.Display(ResultColumns.All, moveInt.FindBest()); moveDT.Display(ResultColumns.All, moveInt.FindBest()); } private static T ElementByElement&lt;T&gt;(T[] arg) { int start = 8; for (int i = smallArraySize - 1; i &gt; start; i--) { arg[i] = arg[i - 1]; } return arg[0]; } private static T BuiltInCopy&lt;T&gt;(T[] arg) { int start = 8; int length = smallArraySize - start - 1; Array.Copy(arg, start, arg, start + 1, length); return arg[0]; } } </code></pre> <p>Here are the results from two runs:</p> <pre><code>f:\MyProgramming\TimSort\Benchmarks\bin\Release&gt;Benchmarks.exe ============ Move part of array right by 1: int ============ Array.Copy() 568475865 0:31.606 1,73 Element by element in a for loop 980013061 0:31.449 1,00 ============ Move part of array right by 1: string ============ Array.Copy() 478224336 0:31.618 2,06 Element by element in a for loop 220168237 0:30.926 4,38 ============ Move part of array right by 1: DateTime ============ Array.Copy() 382906030 0:27.870 2,27 Element by element in a for loop 458265102 0:29.239 1,99 f:\MyProgramming\TimSort\Benchmarks\bin\Release&gt;Benchmarks.exe ============ Move part of array right by 1: int ============ Array.Copy() 500925013 0:28.514 1,76 Element by element in a for loop 988394220 0:31.967 1,00 ============ Move part of array right by 1: string ============ Array.Copy() 483178262 0:30.048 1,92 Element by element in a for loop 193092931 0:27.642 4,43 ============ Move part of array right by 1: DateTime ============ Array.Copy() 450569361 0:30.807 2,11 Element by element in a for loop 568054290 0:31.385 1,71 </code></pre> <p>That is, for <code>int</code> and <code>DateTime</code> <code>ElementByElement</code> is significantly faster; while for <code>string</code> <code>BuiltInCopy</code> is over twice as fast as <code>ElementByElement</code> (and twice as slow as <code>ElementByElement</code> for <code>int</code>). I'd expect the results for <code>int</code> and <code>string</code> to be very similar on a 32-bit machine, since a reference to <code>string</code> on the stack is the same size as an <code>int</code> and no operations other than reading and writing stack memory should be involved.</p>
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    1. POFastest way to move a part of an array to the right
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    1. COmaybe there's a lot of boxing going on? (the arrays using a value-type are slower than those using a reference type...)
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      1. USThomas Danecker
    2. COIn this case I'd expect `Array.Copy` on `int` to be slower than `string`, which it isn't.
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