== Why is this an issue?

The value of a ``++static readonly++`` field is computed at runtime while the value of a ``++const++`` field is calculated at compile time, which improves performance.


This rule raises an issue when a ``++static readonly++`` field is initialized with a value that is computable at compile time.


As specified by Microsoft, the list of types that can have a constant value are:

[frame=all]
[cols="^1,^1"]
|===
|C# type|.Net Fwk type

|bool|System.Boolean
|byte|System.Byte
|sbyte|System.SByte
|char|System.Char
|decimal|System.Decimal
|double|System.Double
|float|System.Single
|int|System.Int32
|uint|System.UInt32
|long|System.Int64
|ulong|System.UInt64
|short|System.Int16
|ushort|System.UInt16
|string|System.String
|===

=== Noncompliant code example

[source,csharp]
----
namespace myLib
{
  public class Foo
  {
    static readonly int x = 1;  // Noncompliant
    static readonly int y = x + 4; // Noncompliant
    static readonly string s = "Bar";  // Noncompliant
  }
}
----


=== Compliant solution

[source,csharp]
----
namespace myLib
{
  public class Foo
  {
    const int x = 1;
    const int y = x + 4;
    const string s = "Bar";
  }
}
----


ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

=== Message

Replace this "static readonly" declaration with "const".


=== Highlighting

the field declaration


endif::env-github,rspecator-view[]