cast()x - a valid expression?

[Steven Schveighoffer]

On Wed, 01 Jun 2011 16:38:42 -0400, KennyTM~ <kennytm at gmail.com> wrote:

> On Jun 2, 11 04:05, Steven Schveighoffer wrote:
>> On Wed, 01 Jun 2011 15:38:32 -0400, Andrej Mitrovic
>> <andrej.mitrovich at gmail.com> wrote:
>>
>>> It seems to do even more than that:
>>>
>>> int a;
>>> const int b;
>>> immutable int c;
>>> shared int d;
>>> shared(const int) e;
>>>
>>> static assert(is(typeof(cast()a) == int));
>>> static assert(is(typeof(cast()b) == int));
>>> static assert(is(typeof(cast()c) == int));
>>> static assert(is(typeof(cast()d) == int));
>>> static assert(is(typeof(cast()e) == int));
>>>
>>> Talk about stealing the storm from std.traits.Unqual..
>>>
>>> On 6/1/11, KennyTM~ <kennytm at gmail.com> wrote:
>>>> While checking the Phobos source I've found an interesting expression
>>>>
>>>> cast()(result[i]) = to!(E)(e);
>>>>
>>>> The 'cast()' means 'cast to mutable', e.g.
>>>>
>>>> class S {}
>>>> void g(S x) {}
>>>> void main() {
>>>> const S s;
>>>> g(cast()s);
>>>> }
>>>>
>>>> But this is not documented in the D spec (CastParam cannot be empty).  
>>>> Is
>>>> this an "accept-invalid" bug, or just a feature not yet documented?
>>>>
>>>>
>>
>> It gets even better:
>>
>> char[] x = "abc".dup;
>>
>> assert(is(typeof(cast(const)x) == const(char[]));
>>
>> I think you may have found a "bug" that should be a feature. It's like
>> dmd is organically growing features that we might need ;) Is this
>> software evolution? Scary!
>>
>> When will dmd decide that human life is a disease to be eradicated? When
>> will the world be dominated by constinators?!!! I fear for my children.
>>
>> All kidding aside, I actually think the syntax makes sense. You are
>> adding/removing modifiers, so just leave the type out of it. The only
>> drawback is, you can't do a cast directly to a tail-const array, but
>> that's not a huge deal, since const(T[]) implicitly casts to const(T)[].
>>
>> I dub this feature "Type Modifier Casting".
>>
>> -Steve
>
> cast(const), cast(immutable) etc are documented. cast() is not. See
> http://d-programming-language.org/expression.html#CastExpression

:O

Of course, by documented, it shows the cast in the grammar (BTW, why the  
separate rule for cast(Type) when CastParam can be Type?), but not in the  
text.  I almost never read the grammar unless I'm confused by the docs.

This is almost as good as const_cast, although it seems too easy to screw  
up and remove const when you don't want to.

-Steve