Readonly field for class type

[Mike Parker]

On Thursday, 15 March 2018 at 10:16:49 UTC, Andrey wrote:
> Hello, is there way to declare read only field for class type 
> with ability to call inner non constant methods? i.e.:
>
>> class A {
>>     int value = 12;
>>     void updateValue() {
>>         value = 13;
>>     }
>> }
>> 
>> class B {
>>     const A a;
>> 
>>     this() {
>>         a = new A();
>>         a.updateValue();  // error: mutable method is not 
>> callable using const object
>>     }
>> }

class A {
     private int _value = 12;

     int value() @property { return _value; }
     void updateValue() { value = 13; }
}

...
auto a = new A();
writeln(a.value);
a.updateValue();
writeln(a.value);