What is the assignment in C in a property signature

Question

I came across some code that said   public int MaxHealth   gt            Memory Address  IsValid             Memory Address  Read lt int gt  Offs Life MaxHp              0    Now I am somewhat familiar with Lambda expressions   I just have not seen it used it this way   What would be the difference between the above statement and   public int MaxHealth    x   y z

User · Accepted Answer

What you re looking at is an expression-bodied member  not a lambda expression   When the compiler encounters an expression-bodied property member  it essentially converts it to a getter like this   public int MaxHealth       get               return Memory Address  IsValid   Memory Address  Read lt int gt  Offs Life MaxHp    0             You can verify this for yourself by pumping the code into a tool called TryRoslyn    Expression-bodied members - like most C  6 features - are just syntactic sugar  This means that they don   t provide functionality that couldn t otherwise be achieved through existing features  Instead  these new features allow a more expressive and succinct syntax to be used  As you can see  expression-bodied members have a handful of shortcuts that make property members more compact    There is no need to use a return statement because the compiler can infer that you want to return the result of the expression There is no need to create a statement block because the body is only one expression There is no need to use the get keyword because it is implied by the use of the expression-bodied member syntax    I have made the final point bold because it is relevant to your actual question  which I will answer now   The difference between        expression-bodied member property public int MaxHealth   gt  x   y z    And        field with field initializer public int MaxHealth   x   y z    Is the same as the difference between     public int MaxHealth       get               return x   y z            And     public int MaxHealth   x   y z    Which - if you understand properties - should be obvious   Just to be clear  though  the first listing is a property with a getter under the hood that will be called each time you access it  The second listing is is a field with a field initializer  whose expression is only evaluated once  when the type is instantiated    This difference in syntax is actually quite subtle and can lead to a  gotcha  which is described by Bill Wagner in a post entitled  A C  6 gotcha  Initialization vs  Expression Bodied Members    While expression-bodied members are lambda expression-like  they are not lambda expressions  The fundamental difference is that a lambda expression results in either a delegate instance or an expression tree  Expression-bodied members are just a directive to the compiler to generate a property behind the scenes  The similarity  more or less  starts and end with the arrow    gt     I ll also add that expression-bodied members are not limited to property members  They work on all these members    Properties Indexers Methods Operators   Added in C  7 0   Constructors Finalizers   However  they do not work on these members    Nested Types Events Fields

User · Answer

It is called Expression Bodied Member and it was introduced in C  6  It is merely syntactic sugar over a get only property   It is equivalent to   public int MaxHealth   get   return Memory Address  IsValid                                Memory Address  Read lt int gt  Offs Life MaxHp    0      An equivalent of a method declaration is avaliable   public string HelloWorld     gt   Hello World     Mainly allowing you shortening of boilerplate

User · Answer

One other significant point if you re using C  6        can be used instead of  get  and is only for  get only  methods - it can t be used with a  set    For C  7  see the comment from  avenmore below - it can now be used in more places  Here s a good reference - https   csharp christiannagel com 2017 01 25 expressionbodiedmembers

User · Answer

This is a new feature of C  6 called an expression bodied member that allows you to define a getter only property using a lambda like function   While it is considered syntactic sugar for the following  they may not produce identical IL   public int MaxHealth       get               return Memory Address  IsValid                    Memory Address  Read lt int gt  Offs Life MaxHp                     0            It turns out that if you compile both versions of the above and compare the IL generated for each you ll see that they are NEARLY the same   Here is the IL for the classic version in this answer when defined in a class named TestClass    property instance int32 MaxHealth          get instance int32 TestClass  get MaxHealth       method public hidebysig specialname      instance int32 get MaxHealth    cil managed           Method begins at RVA 0x2458        Code size 71  0x47       maxstack 2      locals init            0  int32            IL 0000  nop     IL 0001  ldarg 0     IL 0002  ldfld class  mscorlib System Collections Generic Dictionary 2 lt int64  class MemoryAddress gt  TestClass  Memory     IL 0007  ldarg 0     IL 0008  ldfld int64 TestClass  Address     IL 000d  callvirt instance  1 class  mscorlib System Collections Generic Dictionary 2 lt int64  class MemoryAddress gt   get Item  0      IL 0012  ldfld bool MemoryAddress  IsValid     IL 0017  brtrue s IL 001c      IL 0019  ldc i4 0     IL 001a  br s IL 0042      IL 001c  ldarg 0     IL 001d  ldfld class  mscorlib System Collections Generic Dictionary 2 lt int64  class MemoryAddress gt  TestClass  Memory     IL 0022  ldarg 0     IL 0023  ldfld int64 TestClass  Address     IL 0028  callvirt instance  1 class  mscorlib System Collections Generic Dictionary 2 lt int64  class MemoryAddress gt   get Item  0      IL 002d  ldarg 0     IL 002e  ldfld class Offs TestClass  Offs     IL 0033  ldfld class Life Offs  Life     IL 0038  ldfld int64 Life  MaxHp     IL 003d  callvirt instance   0 MemoryAddress  Read lt int32 gt  int64       IL 0042  stloc 0     IL 0043  br s IL 0045      IL 0045  ldloc 0     IL 0046  ret      end of method TestClass  get MaxHealth   And here is the IL for the expression bodied member version when defined in a class named TestClass    property instance int32 MaxHealth          get instance int32 TestClass  get MaxHealth       method public hidebysig specialname      instance int32 get MaxHealth    cil managed           Method begins at RVA 0x2458        Code size 66  0x42       maxstack 2      IL 0000  ldarg 0     IL 0001  ldfld class  mscorlib System Collections Generic Dictionary 2 lt int64  class MemoryAddress gt  TestClass  Memory     IL 0006  ldarg 0     IL 0007  ldfld int64 TestClass  Address     IL 000c  callvirt instance  1 class  mscorlib System Collections Generic Dictionary 2 lt int64  class MemoryAddress gt   get Item  0      IL 0011  ldfld bool MemoryAddress  IsValid     IL 0016  brtrue s IL 001b      IL 0018  ldc i4 0     IL 0019  br s IL 0041      IL 001b  ldarg 0     IL 001c  ldfld class  mscorlib System Collections Generic Dictionary 2 lt int64  class MemoryAddress gt  TestClass  Memory     IL 0021  ldarg 0     IL 0022  ldfld int64 TestClass  Address     IL 0027  callvirt instance  1 class  mscorlib System Collections Generic Dictionary 2 lt int64  class MemoryAddress gt   get Item  0      IL 002c  ldarg 0     IL 002d  ldfld class Offs TestClass  Offs     IL 0032  ldfld class Life Offs  Life     IL 0037  ldfld int64 Life  MaxHp     IL 003c  callvirt instance   0 MemoryAddress  Read lt int32 gt  int64       IL 0041  ret      end of method TestClass  get MaxHealth   See https   msdn microsoft com en-us magazine dn802602 aspx for more information on this and other new features in C  6   See this post Difference between Property and Field in C  3 0  on the difference between a field and a property getter in C    Update   Note that expression-bodied members were expanded to include properties  constructors  finalizers and indexers in C  7 0

User · Answer

You can even write this      private string foo    quot foo quot        private string bar               get   gt    quot  foo bar quot           set                       foo   value

User · Answer

For the following statement shared by Alex Booker in their answer     When the compiler encounters an expression-bodied property member  it essentially converts it to a getter like this    Please see the following screenshot  it shows how this statement  using SharpLab link   public string APIBasePath   gt  Configuration ToolsAPIBasePath    converts to  public string APIBasePath       get               return Configuration ToolsAPIBasePath            Screenshot

User · Answer

Ok    I made a comment that they were different but couldn t explain exactly how but now I know   String Property   get       value     is not the same as   String Property   gt   value     Here s the difference     When you use the auto initializer the property creates the instance of value and uses that value persistently   In the above post there is a broken link to Bill Wagner  that explains this well  and I searched the correct link to understand it myself     In my situation I had my property auto initialize a command in a ViewModel for a View   I changed the property to use expression bodied initializer and the command CanExecute stopped working   Here s what it looked like and here s what was happening   Command MyCommand   get      new Command       works   here s what I changed it to   Command MyCommand   gt  new Command       doesn t work properly   The difference here is when I use   get      I create and reference the SAME command in that property   When I use   gt  I actually create a new command and return it every time the property is called   Therefore  I could never update the CanExecute on my command because I was always telling it to update a new reference of that command       get         same reference   gt             new reference   All that said  if you are just pointing to a backing field then it works fine   This only happens when the auto or expression body creates the return value

[c#] What is the => assignment in C# in a property signature

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