[mattmanser]

I can't upvote this enough.

I done a fair bit of performance problem fixing now in my career and I have never seen a .ToLower be the cause of any client's performance problems. Or really any string manipulation opinion like stringbuilder vs += and all that nonsense.

[LandR]

If you want to get really picky you should be converting to uppercase and ToUpperInvariant in particular:

From C# via the CLR: Important If you want to change the case of a string's characters before performing an ordinal comparison, you should use String’s ToUpperInvariant or ToLowerInvariant method. When normalizing strings, it is highly recommended that you use ToUpperInvariant instead of ToLowerInvariant because Microsoft has optimized the code for performing uppercase comparisons. In fact, the FCL internally normalizes strings to uppercase prior to performing case insensitive comparisons. We use ToUpperInvariant and ToLowerInvariant methods because the String class does not offer ToUpperOrdinal and ToLowerOrdinal methods. We do not use the ToUpper and ToLower methods because these are culture sensitive.

And from MS

CA1308: https://docs.microsoft.com/en-gb/visualstudio/code-quality/c...