Incomplete knowledge + all powerful casts = troubles

[Steven Schveighoffer]

On Mon, 19 Sep 2011 14:01:02 -0400, Steven Schveighoffer  
<schveiguy at yahoo.com> wrote:

> On Mon, 19 Sep 2011 13:54:20 -0400, Trass3r <un at known.com> wrote:
>
>>> Unfortunately now the code contains a small bug. The cast now converts  
>>> const(int)->uint, and foo() will modify a const value, that gives  
>>> undefined effects in D2.
>>
>> I get the point, but in this particular case it's not a real bug since  
>> foo doesn't take it by ref.
>> The int is copied anyways, no matter if the source is const or not.
>>
>> I'm not sure how the actual problem should be solved though...
>>
>>> const(int) x;
>>> auto y = cast(uint)x;
>>> static assert(is(typeof(y) == const(uint)));
>>
>> ...cause this doesn't look right either, cause it silently keeps the  
>> const.
>> Imagine x being unapparently const and you pass y to some function or  
>> template that doesn't allow const.
>> You get an abstruse error message and don't really know why it happened  
>> cause you think y is just a uint.
>>
>> Maybe stripping away constness should be a special case that can't be  
>> combined with a normal cast, i.e. only 'cast()' can do it.
>
> The way it's done in C++, you cannot remove const without a C-style cast  
> or a const_cast.  The above would simply be a compiler error (instead of  
> silently doing what you didn't ask it to do).

Except, of course, the above is not even a valid test case :)  No cast is  
needed, this should work (today):

const(int) x;
uint y = x;

A more relevant case:

const(int) * x;
auto y = cast(uint *)x; // should be an error
auto z = cast(const(uint) *)x; // ok, const isn't being removed.

-Steve