CA1802: Use Literals Where Appropriate

Article
11/14/2023

Property	Value
Rule ID	CA1802
Title	Use Literals Where Appropriate
Category	Performance
Fix is breaking or non-breaking	Non-breaking
Enabled by default in .NET 8	No

Cause

A field is declared static and readonly (Shared and ReadOnly in Visual Basic), and is initialized with a value that is computable at compile time.

By default, this rule only looks at externally visible, static, readonly fields, but this is configurable.

Rule description

The value of a static readonly field is computed at run time when the static constructor for the declaring type is called. If the static readonly field is initialized when it is declared and a static constructor is not declared explicitly, the compiler emits a static constructor to initialize the field.

The value of a const field is computed at compile time and stored in the metadata, which improves run-time performance when it is compared to a static readonly field.

Because the value assigned to the targeted field is computable at compile time, change the declaration to a const field so that the value is computed at compile time instead of at run time.

How to fix violations

To fix a violation of this rule, replace the static and readonly modifiers with the const modifier.

Note

The use of the const modifier is not recommended for all scenarios.

When to suppress warnings

It is safe to suppress a warning from this rule, or disable the rule, if performance is not of 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 CA1802
// The code that's violating the rule is on this line.
#pragma warning restore CA1802

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

[*.{cs,vb}]
dotnet_diagnostic.CA1802.severity = none

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

Configure code to analyze

Use the following options to configure which parts of your codebase to run this rule on.

Include specific API surfaces
Required modifiers

You can configure these options for just this rule, for all rules it applies to, or for all rules in this category (Performance) that it applies to. For more information, see Code quality rule configuration options.

Include specific API surfaces

You can configure which parts of your codebase to run this rule on, based on their accessibility. For example, to specify that the rule should run only against the non-public API surface, add the following key-value pair to an .editorconfig file in your project:

dotnet_code_quality.CAXXXX.api_surface = private, internal

Required modifiers

You can configure this rule to override the required field modifiers. By default, static and readonly are both required modifiers for fields that are analyzed. You can override this to a comma separated listed of one or more modifier values from the below table:

Option Value	Summary
`none`	No modifier requirement.
`static` or `Shared`	Must be declared as 'static' ('Shared' in Visual Basic).
`const`	Must be declared as 'const'.
`readonly`	Must be declared as 'readonly'.

For example, to specify that the rule should run against both static and instance fields, add the following key-value pair to an .editorconfig file in your project:

dotnet_code_quality.CA1802.required_modifiers = none

Example

The following example shows a type, UseReadOnly, that violates the rule and a type, UseConstant, that satisfies the rule.

Imports System

Namespace ca1802

    ' This class violates the rule.
    Public Class UseReadOnly

        Shared ReadOnly x As Integer = 3
        Shared ReadOnly y As Double = x + 2.1
        Shared ReadOnly s As String = "readonly"

    End Class

    ' This class satisfies the rule.
    Public Class UseConstant

        Const x As Integer = 3
        Const y As Double = x + 2.1
        Const s As String = "const"

    End Class

End Namespace

// This class violates the rule.
public class UseReadOnly
{
    static readonly int x = 3;
    static readonly double y = x + 2.1;
    static readonly string s = "readonly";

    public void Print()
    {
        Console.WriteLine(s);
    }
}

// This class satisfies the rule.
public class UseConstant
{
    const int x = 3;
    const double y = x + 2.1;
    const string s = "const";
}

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