String.Equals vs Object.ReferenceEquals (and how string interning can make things fast)

0_results.md

BenchmarkDotNet=v0.12.1, OS=macOS 11.6 (20G165) [Darwin 20.6.0]
Intel Core i5-6267U CPU 2.90GHz (Skylake), 1 CPU, 4 logical and 2 physical cores
.NET Core SDK=5.0.401
  [Host]     : .NET Core 5.0.10 (CoreCLR 5.0.1021.41214, CoreFX 5.0.1021.41214), X64 RyuJIT
  DefaultJob : .NET Core 5.0.10 (CoreCLR 5.0.1021.41214, CoreFX 5.0.1021.41214), X64 RyuJIT

Method	Mean	Error	StdDev
StringEquals	7.3439 ns	0.0302 ns	0.0252 ns
ReferenceEquals	0.0600 ns	0.0034 ns	0.0032 ns

benchmark.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net5.0</TargetFramework>
    <OutputType>Exe</OutputType>
  </PropertyGroup>
  <PropertyGroup>
    <PlatformTarget>AnyCPU</PlatformTarget>
    <DebugType>pdbonly</DebugType>
    <DebugSymbols>true</DebugSymbols>
    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
    <Optimize>true</Optimize>
    <Configuration>Release</Configuration>
    <IsPackable>false</IsPackable>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="BenchmarkDotNet" Version="0.12.1" />
    <PackageReference Include="BenchmarkDotNet.Diagnostics.Windows" Version="0.12.1" Condition="'$(OS)' == 'Windows_NT'"/>
  </ItemGroup>
</Project>

Benchmarks.cs

using System;
using BenchmarkDotNet;
using BenchmarkDotNet.Attributes;

namespace string_comparison_bench
{
    public class Benchmarks
    {
        private string str1 = "string1";
        private string str2 = "string2";

        [Benchmark]
        public bool StringEquals()
        {
            return str1.Equals(str1) && str1.Equals(str2);
        }

        [Benchmark]
        public bool ReferenceEquals()
        {
            return ReferenceEquals(str1, str1) && ReferenceEquals(str1, str2);
        }
    }
}

Program.cs

using BenchmarkDotNet.Running;

namespace string_comparison_bench
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var summary = BenchmarkRunner.Run<Benchmarks>();
        }
    }
}