CA1858: Use StartsWith instead of IndexOf

#Cause

System.String.IndexOf is called and its result is compared against zero.

#Rule description

It's more efficient and clearer to call System.String.StartsWith than to call System.String.IndexOf and compare the result with zero to determine whether a string starts with a given prefix.

IndexOf searches the entire string, while StartsWith only compares at the beginning of the string.

#How to fix violations

Replace the call to System.String.IndexOf with a call to System.String.StartsWith.

#Example

The following code snippet shows a violation of CA1858:

bool M(string s)
{
    return s.IndexOf("abc") == 0;
}

Function M(s As String) As Boolean
    Return s.IndexOf("abc") = 0
End Function

The following code snippet fixes the violation:

bool M(string s)
{
    return s.StartsWith("abc");
}

Function M(s As String) As Boolean
    Return s.StartsWith("abc")
End Function

#When to suppress warnings

It's safe to suppress this warning if performance isn't a concern.

#Suppress a warning

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

#pragma warning disable CA1858
// The code that's violating the rule is on this line.
#pragma warning restore CA1858

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

[*.{cs,vb}]
dotnet_diagnostic.CA1858.severity = none

For more information, see How to suppress code analysis warnings.