Private enum members + Descent

[Lars T. Kyllingstad]

Yigal Chripun wrote:
> Lars T. Kyllingstad Wrote:
> 
>> I was going to protest: "But what about const struct members? Should the 
>> size of the following struct depend on whether the compiler determines 
>> it can optimize by turning its const member into a manifest constant?"
>>
>>    struct Foo { const int bar = 123; }
>>
>> But then I decided to actually try it with the current DMD2, and found 
>> that the compiler does just that!
>>
>>    writeln(Foo.sizeof);    // Prints "1", not "4"
>>
>>    Foo foo;
>>    auto p = &foo.bar;   // Error: constant 123 is not an lvalue
>>
>> What's going on? Is this intended behaviour?
>>
>> -Lars
> 
> what D version?

DMD 2.035.


> in D1 const is a manifest constant as far as I know. 

Yes, but in D2 the spec says that const is a constant view of mutable 
data. There isn't (or at least I can't find) mention that struct members 
are excepted from this rule.


> to answer to general question, "what about structs": 
> I'd say that the same rules should apply just like inside functions. 
> 
> struct Foo { const int num = 42; } // num should be a manifest const
> 
> can you give a use-case/example where you wouldn't want to do that but rather store the constant in the struct? 

In any case where a different view of the same data is non-const. Or 
would you also disallow casting away const-ness?

-Lars