use collection expression spread operator

[testfirstcoder]

• avoid additional array allocation and conversion
• avoid implicit checking of duplicates using Union method

[mikeminutillo]

Hi @testfirstcoder ,

You raised a similar PR last week #6969

That one was closed as not deduplicating, which this one also does not do.

What issue are you trying to fix with these changes?

[testfirstcoder]

Hi @mikeminutillo,

it's not a particular issue fixing but rather a performance related one.

[SimpleJob(RuntimeMoniker.Net80)]
[MemoryDiagnoser]
public class Benchmark
{
    private int[] visitedNodes;

    private const int NewNode = -1;

    [Params(0, 1, 10)]
    public int N;

    public Benchmark() => visitedNodes = Enumerable.Range(start: 1, count: N).ToArray();

    [Benchmark]
    public void Union_ToArray()
    {
        int[] newVisitedNodes = visitedNodes.Union(new[] { NewNode }).ToArray();
    }

    [Benchmark]
    public void Append_ToArray()
    {
        int[] newVisitedNodes = visitedNodes.Append(NewNode).ToArray();
    }

    [Benchmark]
    public void Collection_Expression_Spread_Operator()
    {
        int[] newVisitedNodes = [.. visitedNodes, NewNode];
    }
}

void Main() => BenchmarkRunner.Run<Benchmark>();

// * Summary *

BenchmarkDotNet v0.13.12, Windows 10 (10.0.19045.4170/22H2/2022Update)
Intel Core i7-10700 CPU 2.90GHz, 1 CPU, 16 logical and 8 physical cores
.NET SDK 8.0.202
[Host] : .NET 8.0.3 (8.0.324.11423), X64 RyuJIT AVX2

Job=.NET 8.0 Runtime=.NET 8.0

Method	N	Mean	Error	StdDev	Median	Gen0	Allocated
Union_ToArray	0	83.037 ns	1.6542 ns	1.6988 ns	83.384 ns	0.0401	336 B
Append_ToArray	0	47.313 ns	0.8261 ns	0.7727 ns	47.171 ns	0.0105	88 B
Collection_Expression_Spread_Operator	0	4.394 ns	0.1457 ns	0.4296 ns	4.241 ns	0.0038	32 B
Union_ToArray	1	79.278 ns	1.4234 ns	2.9077 ns	79.304 ns	0.0401	336 B
Append_ToArray	1	49.852 ns	0.8911 ns	1.1587 ns	50.158 ns	0.0105	88 B
Collection_Expression_Spread_Operator	1	4.527 ns	0.1248 ns	0.3622 ns	4.508 ns	0.0038	32 B
Union_ToArray	10	78.397 ns	1.5664 ns	2.3446 ns	78.125 ns	0.0401	336 B
Append_ToArray	10	46.757 ns	0.9523 ns	2.0087 ns	46.258 ns	0.0105	88 B
Collection_Expression_Spread_Operator	10	4.166 ns	0.1129 ns	0.3203 ns	4.089 ns	0.0038	32 B

[testfirstcoder]

Is an implicit deduplication using Union necessary? Could visitedNodes have some duplicates?

There is an explicit duplication check here, isn't?

if (visitedNodes.Any(n => n == node))
{
    return true;
}