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Initialize reference type static fields inline







Breaking Change

Non Breaking

A reference type declares an explicit static constructor.

When a type declares an explicit static constructor, the just-in-time (JIT) compiler adds a check to each of the type's static methods and instance constructors to ensure that the static constructor was previously called. Static initialization is triggered when any static member is accessed or when an instance of the type is created. However, static initialization is not triggered if you declare a variable of the type but do not use it, which can be important if the initialization changes global state.

When all static data is initialized inline and an explicit static constructor is not declared, Microsoft intermediate language (MSIL) compilers add the beforefieldinit flag and an implicit static constructor, which initializes the static data, to the MSIL type definition. When the JIT compiler encounters the beforefieldinit flag, in most cases the static constructor checks are not added. Static initialization is guaranteed to occur at some time before any of the static fields are accessed but not before a static method or instance constructor is invoked. Note that static initialization can occur at any time after a variable of the type is declared.

Static constructor checks can reduce performance. Often a static constructor is used only to initialize static fields, in which case it is only necessary to ensure that static initialization occurs before the first access of a static field. The beforefieldinit behavior is appropriate for these and most other types. It is only inappropriate when static initialization affects global state and one of the following is true:

  • The effect on global state is expensive and is not needed if the type is not used.

  • The global state effects can be accessed without accessing any static fields of the type.

To fix a violation of this rule, initialize all static data when it is declared and remove the static constructor.

It is safe to suppress a warning from this rule if performance is not a concern; or if global state changes due to static initialization are expensive, or must be guaranteed to occur before a static method of the type is called or an instance of the type is created.

The following example shows a type, StaticConstructor, that violates the rule and a type, NoStaticConstructor, that replaces the static constructor with inline initialization to satisfy the rule.

Imports System
Imports System.Resources

Namespace PerformanceLibrary

   Public Class StaticConstructor

      Shared someInteger As Integer 
      Shared resourceString As String  

      Shared Sub New()

         someInteger = 3
         Dim stringManager As New ResourceManager("strings", _
         resourceString = stringManager.GetString("string")

      End Sub 

   End Class 

   Public Class NoStaticConstructor

      Shared someInteger As Integer = 3
      Shared resourceString As String = InitializeResourceString()

      Shared Private Function InitializeResourceString()

         Dim stringManager As New ResourceManager("strings", _
         Return stringManager.GetString("string")

      End Function 

   End Class 

End Namespace

Note the addition of the beforefieldinit flag on the MSIL definition for the NoStaticConstructor class.

.class public auto ansi StaticConstructor extends [mscorlib]System.Object { } // end of class StaticConstructor .class public auto ansi beforefieldinit NoStaticConstructor extends [mscorlib]System.Object { } // end of class NoStaticConstructor