Compiler Error CS0191

Property or indexer 'name' cannot be assigned to -- it is read only

A readonly field can only take an assignment in a constructor or at declaration. For more information, see Constructors.

CS0191 also results if the readonly field is static and the constructor is not marked static.

Example

The following sample generates CS0191.

// CS0191.cs  
class MyClass  
{  
    public readonly int TestInt = 6;  // OK to assign to readonly field in declaration  
  
    MyClass()  
    {  
        TestInt = 11; // OK to assign to readonly field in constructor  
    }  
  
    public void TestReadOnly()  
    {  
        TestInt = 19;                  // CS0191  
    }  
  
    public static void Main()  
    {  
    }  
}