Stop Using string.ToLowerInvariant() to Compare Strings. InvariantCulture Comparisons are Slow
by darren horrocksA lot of people use ToLower() or ToLowerInvariant() to normalise their strings before comparing them with ==, STOP IT.
This is very slow, and while that may not matter for 1 or 2 string comparasons, it mounts up in large projects.
While there is a very small use case for using Invariant Culture, unless you are absolutely certain that you need it, and why you need it, then you do not need it.
These tests in github aim to show what we should be using instead.
Each test was ran 100,000,000 times, which is a realistic number of records that could be compared in a loop.
| Test | Time in ms |
|---|---|
| ToLowerInvariant | 2667 ms |
| ToUpperInvariant | 2302 ms |
| DOUBLE ToLowerInvariant | 3864 ms |
| Equals (NoOptions) (as a control test) | 426 ms |
| Equals (InvariantCultureIgnoreCase) | 14891 ms |
| Equals (CurrentCultureIgnoreCase) | 14605 ms |
| Equals (OrdinalIgnoreCase) | 1168 ms |
As you can see, Equals with OrdinalIgnoreCase is an order of magnitude faster than InvariantCultureIgnoreCase, and about twice as fast (half as slow) as ToLowerInvariant. Stop using Invariant unless you absolutely understand your use case for it.
