Automatically implemented property in struct can not be assigned

Question

I have a next code:

struct T  {     public T(int u)      {          this.U = 10; //Errors are here     }      public int U { get; private set;  } } 

C# compiler give me a pair of errors in stated line: 1) Backing field for automatically implemented property 'TestConsoleApp.Program.T.U' must be fully assigned before control is returned to the caller. Consider calling the default constructor from a constructor initializer. 2) The 'this' object cannot be used before all of its fields are assigned to

What I do wrong? Help me understand.

Answer 1

From the C# Specification:

10.7.3 Automatically implemented properties

When a property is specified as an automatically implemented property, a hidden backing field is automatically available for the property, and the accessors are implemented to read from and write to that backing field.

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Because the backing field is inaccessible, it can be read and written only through the property accessors, even within the containing type.

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This restriction also means that definite assignment of struct types with auto-implemented properties can only be achieved using the standard constructor of the struct, since assigning to the property itself requires the struct to be definitely assigned. This means that user-defined constructors must call the default constructor.

So you need this:

struct T  {     public T(int u)         : this()     {          this.U = u;     }      public int U { get; private set; } }