CA1861: Avoid constant arrays as arguments
| Property | Value |
|---|---|
| Rule ID | CA1861 |
| Title | Avoid constant arrays as arguments |
| Category | Performance |
| Fix is breaking or non-breaking | Non-breaking |
| Enabled by default in .NET 9 | As suggestion |
Cause
A constant array of literal values is passed to a method via regular invocation or extension method invocation.
Rule description
Constant arrays passed as arguments are not reused when called repeatedly, which implies a new array is created each time. If the passed array is not mutated within the called method, consider extracting it to a static readonly field to improve performance.
Note
If the called method mutates the passed array or if you're not sure if the method would mutate the array, don't extract the array to a static readonly field. Doing so could be a breaking change. In this case, it's better to suppress the warning instead.
How to fix violations
Extract constant arrays to static readonly fields if the passed array is not mutated within the called method.
The following example shows a violation of the rule:
// A method argument
string message = string.Join(" ", new[] { "Hello", "world!" });
' A method argument
Dim message As String = String.Join(" ", {"Hello", "world!"})
The following example show how the violation of this rule is fixed by extracting the argument to a static readonly field.
private static readonly string[] array = new[] { "Hello" , "world!" };
private string GetMessage()
{
return string.Join(" ", array);
}
Private Shared ReadOnly array As String() = {"Hello", "world!"}
Private Function GetMessage() As String
Return String.Join(" ", array)
End Function
Now, the value of the array is resolved at compile time rather than at run time, making code more performant.
When to suppress warnings
Suppress a violation of this rule if:
- The invocation only runs once.
- The array could be mutated within the invoked method, or you aren't sure if it would mutated.
- You're not concerned about the performance impact of creating a constant array for each invocation.
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 CA1861
// The code that's violating the rule is on this line.
#pragma warning restore CA1861
To disable the rule for a file, folder, or project, set its severity to none in the configuration file.
[*.{cs,vb}]
dotnet_diagnostic.CA1861.severity = none
For more information, see How to suppress code analysis warnings.
