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Code Analyzer for C#

There is a newer version: 10.2.0.105762

Why is this an issue?
Certain characters, once normalized to lowercase, cannot make a round trip. That is, they can not be converted from one locale to another and then
accurately restored to their original characters.
It is therefore strongly recommended to normalize characters and strings to uppercase instead.
Noncompliant code example
Thread.CurrentThread.CurrentCulture = new CultureInfo("tr-TR");
var areStringEqual = "INTEGER".ToLower() == "integer"; // Noncompliant, the result is false as the ToLower will resolve to "ınteger"
var areCharEqual = char.ToLower('I') == 'i'; // Noncompliant, the result is false as the ToLower will resolve to "ı"

var incorrectRoundtrip = "İ".ToLowerInvariant().ToUpper() == "I".ToLowerInvariant().ToUpper(); // Noncompliant, because of the lower we lose the information about the correct uppercase character

Compliant solution
Thread.CurrentThread.CurrentCulture = new CultureInfo("tr-TR");
var areStringEqual = "ınteger".ToUpperInvariant() == "ıNTEGER";
var areCharEqual = char.ToUpperInvariant('ı') == 'ı';
var correctRoundtrip = "İ".ToUpperInvariant().ToLower() != "I".ToUpperInvariant().ToLower();

Resources

   Internationalization for Turkish 
   How to correctly normalize
  strings 
   Best Practices
  for Using Strings in .NET