InternedString

Represents a string which is guaranteed to be interned.

Provides an optimized GetHashCode() and Equals(...) overrides, which rely on reference comparison rather than string contents.

Usage:

// O(n) operation happens only here, so we want to re-use this object
var iString = new InternedString("typically_a_very_long_string_key");

// now any call to `GetHashCode()` and `Equals(...)` will run in a constant time
mySet.Add(iString);

Benchmark

The purpose of this benchmark is to find out, how a simple HashSet<string>.Contains(...) method performace can be affected by a string length.

BenchmarkDotNet=v0.12.0, OS=Windows 10.0.18362
Intel Core i7-7820HQ CPU 2.90GHz (Kaby Lake), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=3.0.100
  [Host]     : .NET Core 3.0.0 (CoreCLR 4.700.19.46205, CoreFX 4.700.19.46214), X64 RyuJIT
  DefaultJob : .NET Core 3.0.0 (CoreCLR 4.700.19.46205, CoreFX 4.700.19.46214), X64 RyuJIT

Method	StringLength	Mean	Error	StdDev
String	4	19.38 ns	0.115 ns	0.102 ns
InternedString	4	15.20 ns	0.068 ns	0.063 ns
String	8	21.60 ns	0.049 ns	0.044 ns
InternedString	8	15.22 ns	0.083 ns	0.078 ns
String	16	26.69 ns	0.143 ns	0.134 ns
InternedString	16	15.18 ns	0.045 ns	0.042 ns
String	32	35.76 ns	0.121 ns	0.113 ns
InternedString	32	15.25 ns	0.106 ns	0.099 ns
String	64	57.77 ns	0.121 ns	0.107 ns
InternedString	64	15.30 ns	0.108 ns	0.101 ns
String	128	104.26 ns	0.634 ns	0.495 ns
InternedString	128	15.22 ns	0.070 ns	0.065 ns
String	256	195.68 ns	0.466 ns	0.364 ns
InternedString	256	16.44 ns	0.353 ns	0.599 ns
String	512	380.49 ns	0.718 ns	0.671 ns
InternedString	512	15.23 ns	0.077 ns	0.072 ns
String	1024	744.70 ns	1.089 ns	0.965 ns
InternedString	1024	15.23 ns	0.089 ns	0.084 ns
String	2048	1,480.07 ns	8.714 ns	7.725 ns
InternedString	2048	15.21 ns	0.058 ns	0.054 ns
String	4096	2,935.76 ns	6.445 ns	5.714 ns
InternedString	4096	15.18 ns	0.039 ns	0.033 ns
String	8192	5,862.37 ns	9.224 ns	8.177 ns
InternedString	8192	15.22 ns	0.092 ns	0.086 ns
String	16384	11,731.94 ns	38.340 ns	35.864 ns
InternedString	16384	15.19 ns	0.052 ns	0.048 ns
String	32768	23,415.15 ns	49.521 ns	46.322 ns
InternedString	32768	15.19 ns	0.068 ns	0.063 ns
String	65536	48,998.99 ns	881.609 ns	1,264.377 ns
InternedString	65536	15.87 ns	0.182 ns	0.170 ns
String	131072	98,211.13 ns	1,952.642 ns	3,419.895 ns
InternedString	131072	16.05 ns	0.159 ns	0.149 ns