How to break const

[Timon Gehr]

On 06/20/2012 05:33 PM, deadalnix wrote:
> Le 20/06/2012 17:24, Timon Gehr a écrit :
>> On 06/20/2012 05:17 PM, deadalnix wrote:
>>> Le 20/06/2012 16:55, Timon Gehr a écrit :
>>>>>> It works if implicit conversions from 'R delegate(A)' to
>>>>>> 'R delegate(A) const' are allowed, as well as looking up an
>>>>>> 'R delegate(A) in a const receiver object.
>>>>>
>>>>> What about conversion from/to immutable ?
>>>>
>>>> Simple application of transitivity. This part is the same for 1./2.
>>>>
>>>> 'R delegate(A)' and 'R delegate(A) const' are not convertible to
>>>> 'R delegate(A) immutable', but 'R delegate(A) immutable' is
>>>> convertible to 'R delegate(A)' and 'R delegate(A) const'.
>>>>
>>>> 'R delegate(A)' and 'R delegate(A) const' decay to
>>>> 'R delegate(A) immutable' when stored in an immutable object.
>>>>
>>>
>>> I've gone through a similar reasoning. It does not work.
>>
>> Yes it does.
>>
>>> Here are implicit casts summed up :
>>>
>>> mutable -> const
>>> immutable -> const
>>> immutable -> mutable
>>>
>>> which implicitely imply immutable -> const
>>>
>>> And then you add when storing in immutable object.
>>>
>>> mutable -> immutable
>>> const -> immutable
>>>
>>
>> These are not valid implicit conversions.
>>
>> What I meant was:
>>
>> struct S{
>> R delegate(A) mutable;
>> R delegate(B)const const_;
>> }
>>
>> static assert(is(typeof(immutable(S).mutable)==R delegate(A) immutable));
>> static assert(is(typeof(immutable(S).const_)==R delegate(A) immutable));
>>
>>
>>> It means that you can store a delegate that have a mutable frame pointer
>>> into an immutable object, which break transitivity.
>>
>> No.
>
> OK I understand.
>
> This is consistent for the frame pointer type qualifier. But not for the
> function pointer. Remember that the function pointer accept the frame
> pointer as argument.
>
> This set of rule prevent safe closure rebinding.

There is no such thing as safe closure rebinding.