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HLQ004_RefEnumerationVariable.md

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HLQ004: The enumerator returns a reference to the item.

Cause

The enumerator returns a reference to the items. The enumeration variable is not declared as a reference so a copy of each item will be made.

Severity

Warning

Rule description

Benchmarks

The following benchmarks compare the performance of the enumerator returning a reference to the item and the enumerator returning a copy of the item.

Source: https://github.com/NetFabric/NetFabric.Hyperlinq.Analyzer/blob/master/NetFabric.Hyperlinq.Analyzer.Benchmarks/HLQ004_RefEnumerationVariable.cs


BenchmarkDotNet v0.13.6, Windows 10 (10.0.19045.3269/22H2/2022Update)
Intel Core i7-7567U CPU 3.50GHz (Kaby Lake), 1 CPU, 4 logical and 2 physical cores
.NET SDK 8.0.100-preview.5.23303.2
  [Host] : .NET 6.0.20 (6.0.2023.32017), X64 RyuJIT AVX2
  .NET 6 : .NET 6.0.20 (6.0.2023.32017), X64 RyuJIT AVX2
  .NET 7 : .NET 7.0.8 (7.0.823.31807), X64 RyuJIT AVX2
  .NET 8 : .NET 8.0.0 (8.0.23.28008), X64 RyuJIT AVX2
Method Job Runtime Count Mean Error StdDev Median Ratio RatioSD Allocated Alloc Ratio
Copy .NET 6 .NET 6.0 100 194.52 ns 13.354 ns 39.373 ns 193.28 ns baseline **** - NA
Ref .NET 6 .NET 6.0 100 106.87 ns 4.638 ns 13.676 ns 104.42 ns 1.86x faster 0.48x - NA
Copy .NET 7 .NET 7.0 100 107.09 ns 3.389 ns 9.669 ns 105.55 ns baseline - NA
Ref .NET 7 .NET 7.0 100 88.28 ns 0.885 ns 0.739 ns 88.25 ns 1.23x faster 0.09x - NA
Copy .NET 8 .NET 8.0 100 143.37 ns 1.121 ns 0.875 ns 143.33 ns baseline - NA
Ref .NET 8 .NET 8.0 100 74.84 ns 3.139 ns 9.007 ns 69.55 ns 1.98x faster 0.19x - NA
Copy .NET 6 .NET 6.0 10000 8,137.04 ns 50.933 ns 47.643 ns 8,131.04 ns baseline **** - NA
Ref .NET 6 .NET 6.0 10000 6,775.81 ns 97.054 ns 99.667 ns 6,767.92 ns 1.20x faster 0.02x - NA
Copy .NET 7 .NET 7.0 10000 13,655.17 ns 219.651 ns 183.418 ns 13,596.77 ns baseline - NA
Ref .NET 7 .NET 7.0 10000 8,157.08 ns 154.674 ns 151.911 ns 8,109.30 ns 1.68x faster 0.02x - NA
Copy .NET 8 .NET 8.0 10000 13,881.05 ns 255.603 ns 566.399 ns 13,637.18 ns baseline - NA
Ref .NET 8 .NET 8.0 10000 6,117.83 ns 87.811 ns 77.842 ns 6,129.23 ns 2.27x faster 0.09x - NA

How to fix violations

Add the keywords 'ref' of 'ref readonly' before the 'var' keyword of variable type.

When to suppress warnings

Should not be suppressed.

Example of a violation

var span = new ReadOnlySpan<int>(new[] { 0, 1, 2, 3, 4, 5 });

foreach(var item in span)
    Console.WriteLine(item);

Example of how to fix

var span = new ReadOnlySpan<int>(new[] { 0, 1, 2, 3, 4, 5 });

foreach(ref readonly var item in span)
    Console.WriteLine(item);