What is the use of static constructors

Question

Please explain to me the use of static constructor  Why and when would we create a static constructor and is it possible to overload one

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1 It can only access the static member s  of the class   Reason   Non static member is specific to the object instance  If static constructor are allowed to work on non static members it will reflect the changes in all the object instance  which is impractical   2 There should be no parameter s  in static constructor   Reason  Since  It is going to be called by CLR  nobody can pass the parameter to it  3 Only one static constructor is allowed   Reason  Overloading needs the two methods to be different in terms of method constructor definition which is not possible in static constructor   4 There should be no access modifier to it   Reason  Again the reason is same call to static constructor is made by CLR and not by the object  no need to have access modifier to it

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No you can t overload it  a static constructor is useful for initializing any static fields associated with a type  or any other per-type operations  - useful in particular for reading required configuration data into readonly fields  etc   It is run automatically by the runtime the first time it is needed  the exact rules there are complicated  see  beforefieldinit    and changed subtly between CLR2 and CLR4   Unless you abuse reflection  it is guaranteed to run at most once  even if two threads arrive at the same time

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Static constructors are also very useful when you have static fields that rely upon each other such that the order of initialization is important   If you run your code through a formatter beautifier that changes the order of the fields then you may find yourself with null values where you didn t expect them   Example  Suppose we had this class   class ScopeMonitor       static string urlFragment    foo bar       static string firstPart   http   www example com        static string fullUrl  firstPart   urlFragment      When you access fullUr  it will be  http   www example com foo bar    Months later you re cleaning up your code and alphabetize the fields  let s say they re part of a much larger list  so you don t notice the problem   You have   class ScopeMonitor       static string firstPart   http   www example com        static string fullUrl  firstPart   urlFragment      static string urlFragment    foo bar       Your fullUrl value is now just  http   www example com   since urlFragment hadn t been initialized at the time fullUrl was being set   Not good   So  you add a static constructor to take care of the initialization   class ScopeMonitor       static string firstPart   http   www example com        static string fullUrl      static string urlFragment    foo bar        static ScopeMonitor                 fullUrl  firstPart   urlFragment             Now  no matter what order you have the fields  the initialization will always be correct

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you can use static constructor to initializes static fields  It runs at an indeterminate time before those fields are used  Microsoft s documentation and many developers warn that static constructors on a type impose a substantial overhead  It is best to avoid static constructors for maximum performance   update  you can t use more than one static constructor in the same class  however you can use other instance constructors with  maximum  one static constructor

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From Static Constructors  C  Programming Guide    A static constructor is used to initialize any static data  or to perform a particular action that needs performed once only  It is called automatically before the first instance is created or any static members are referenced  Static constructors have the following properties   A static constructor does not take access modifiers or have parameters   A static constructor is called automatically to initialize the class before the first instance is created or any static members are referenced   A static constructor cannot be called directly   The user has no control on when the static constructor is executed in the program   A typical use of static constructors is when the class is using a log file and the constructor is used to write entries to this file   Static constructors are also useful when creating wrapper classes for unmanaged code  when the constructor can call the LoadLibrary method

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Static constructor called only the first instance of the class created  and used to perform a particular action that needs to be performed only once in the life cycle of the class

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Why and when would we create a static constructor        One specific reason to use a static constructor is to create a  super enum  class  Here s a  simple  contrived  example   public class Animals       private readonly string  description      private readonly string  speciesBinomialName       public string Description   get   return  description          public string SpeciesBinomialName   get   return  speciesBinomialName           private Animals string description  string speciesBinomialName                 description   description           speciesBinomialName   speciesBinomialName             private static readonly Animals  dog      private static readonly Animals  cat      private static readonly Animals  boaConstrictor       public static Animals Dog   get   return  dog          public static Animals Cat   get   return  cat          public static Animals BoaConstrictor   get   return  boaConstrictor           static Animals                  dog   new Animals  Man s best friend    Canis familiaris             cat   new Animals  Small  typically furry  killer    Felis catus             boaConstrictor   new Animals  Large  heavy-bodied snake    Boa constrictor              You d use it very similarly  in syntactical appearance  to any other enum   Animals Dog   The advantage of this over a regular enum is that you can encapsulate related info easily  One disadvantage is that you can t use these values in a switch statement  because it requires constant values

[c#] What is the use of static constructors?

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