When should use Readonly and Get only properties

Question

In a  NET application when should I use  ReadOnly  properties and when should I use just  Get   What is the difference between these two   private readonly double Fuel  0   public double FuelConsumption       get               return Fuel                    or  private double Fuel  0   public double FuelConsumption        get                  return Fuel

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Methods suggest something has to happen to return the value  properties suggest that the value is already there   This is a rule of thumb  sometimes you might want a property that does a little work  i e  Count   but generally it s a useful way to decide

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Creating a property with only a getter makes your property read-only for any code that is outside the class   You can however change the value using methods provided by your class    public class FuelConsumption       private double fuel      public double Fuel               get   return this fuel              public void FillFuelTank double amount                this fuel    amount           public static void Main         FuelConsumption f   new FuelConsumption         double a      a   f Fuel     Will work     f Fuel   a     Does not compile      f FillFuelTank 10      Value is changed from the method s code     Setting the private field of your class as readonly allows you to set the field value only once  using an inline assignment or in the class constructor   You will not be able to change it later   public class ReadOnlyFields       private readonly double a   2 0      private readonly double b       public ReadOnlyFields                 this b   4 0            readonly class fields are often used for variables that are initialized during class construction  and will never be changed later on   In short  if you need to ensure your property value will never be changed from the outside  but you need to be able to change it from inside your class code  use a  Get-only  property   If you need to store a value which will never change once its initial value has been set  use a readonly field

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A property that has only a getter is said to be readonly  Cause no setter is provided  to change the value of the property  from outside    C  has has a keyword readonly  that can be used on fields  not properties   A field that is marked as  readonly   can only be set once during the construction of an object  in the constructor    private string  name    Foo      field for property Name  private bool  enabled   false     field for property Enabled   public string Name     This is a readonly property    get       return  name           public bool Enabled     This is a read- and writeable property    get      return  enabled        set       enabled   value

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As of C  6 you can declare and initialise a  read-only auto-property  in one line   double FuelConsumption   get      2    You can set the value from the constructor but not other methods

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readonly properties are used to create a fail-safe code  i really like the Encapsulation posts series of Mark Seemann about properties and backing fields   http   blog ploeh dk 2011 05 24 PokayokeDesignFromSmellToFragrance aspx  taken from Mark s example   public class Fragrance   IFragrance       private readonly string name       public Fragrance string name                if  name    null                        throw new ArgumentNullException  name                       this name   name             public string Spread                 return this name            in this example you use the readonly name field to make sure the class invariant is always valid  in this case the class composer wanted to make sure the name field is set only once  immutable  and is always present

[c#] When should use Readonly and Get only properties

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