CA1862: Use the 'StringComparison' method overloads to perform case-insensitive string comparisons

Cause

Code compares two strings in a case-insensitive manner by first calling System.String.ToLower, System.String.ToLowerInvariant, System.String.ToUpper, or System.String.ToUpperInvariant on one or both strings.

When code calls System.String.ToLower, System.String.ToLowerInvariant, System.String.ToUpper, or System.String.ToUpperInvariant, an allocation is performed. If the only reason for calling these methods is to perform a case-insensitive string comparison or search, the allocation is unnecessary. Instead, you can call a string comparison method that takes a System.StringComparison and specify one of the *IgnoreCase values.

The following example shows a violation of the rule:

csharp

string s1 = "aBc";
string s2 = "aBC";

int _ = s1.ToUpper().CompareTo(s2.ToUpper());

Dim s1 As String = "aBc"
Dim s2 As String = "aBC"

Dim i As Integer = s1.ToUpper().CompareTo(s2.ToUpper())

The following example shows code that fixes the violation:

csharp

string s1 = "aBc";
string s2 = "aBC";

int _ = StringComparer.CurrentCultureIgnoreCase.Compare(s1, s2);

Dim s1 As String = "aBc"
Dim s2 As String = "aBC"

Dim i As Integer = StringComparer.CurrentCultureIgnoreCase.Compare(s1, s2)

It's safe to suppress warnings from this rule if performance isn't a concern.

If you're using Entity Framework Core (EF Core), you should suppress this rule for scenarios where you're querying a database by comparing a string. EF Core throws an exception if you use a method such as System.String.Equals(System.String,System.StringComparison) that takes a System.StringComparison argument, as it won't translate such queries to SQL. For more information, see Translation of built-in .NET string operations.

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

csharp

#pragma warning disable CA1862
// The code that's violating the rule is on this line.
#pragma warning restore CA1862

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

ini

[*.{cs,vb}]
dotnet_diagnostic.CA1862.severity = none