How to break const

[Christophe Travert]

Timon Gehr , dans le message (digitalmars.D:170288), a écrit :
> On 06/20/2012 09:16 AM, deadalnix wrote:
>> Le 19/06/2012 17:49, Timon Gehr a écrit :
>>>
>>> The question is, what the meaning of 'const' references should be:
>>>
>>> 1. data cannot be changed transitively through the reference
>>>
>>> 2. the reference can reference both 'const' and 'immutable' data and
>>> 'immutable' data can transitively not be changed through the
>>> reference.
>>>
>>>
>>> 1. requires transitive const for delegate context pointers, 2. does not.
>>>
>>
>> No, 2. require 1., even if the initialization is broken.
>>
>> class Foo {
>>      void delegate() dg;
>>
>>      this(immutable void delegate() dg) immutable {
>>          thid.dg = dg;
>>      }
>> }
>>
>> Now, as delegate doesn't carry the constness of its context, an
>> immutable instance of Foo can refers to something that isn't immutable.
> 
> Clarification: 'const' means 'const'. No other qualifiers.
>
> There is no 'const' in that example code. 'immutable' obviously needs to 
> be transitive regardless of the particular interpretation of 'const'.
> 
const means: maybe immutable. Thus const needs to be transitive too. If 
you apply different rules to const and to immutable, you are breaking 
the consistency of the langage.