Re: Use conditional casting with symtab_node

[Gabriel Dos Reis <gdr@integrable-solutions.net>]

On Wed, Sep 19, 2012 at 1:39 PM, Lawrence Crowl <crowl@googlers.com> wrote:
> On 9/19/12, Gabriel Dos Reis <gdr@integrable-solutions.net> wrote:
>> On Sep 19, 2012 Richard Guenther <richard.guenther@gmail.com> wrote:
>> > Indeed.  Btw, can we not provide a specialization for
>> > dynamic_cast <>?  This ->try_... looks awkward to me compared
>> > to the more familiar
>> >
>> > vnode = dynamic_cast <varpool_node> (node)
>> >
>> > but yeah - dynamic_cast is not a template ... (but maybe there
>> > is some standard library piece that mimics it?).
>>
>> No, it is a language primitive.
>>
>> but we can define out own operation with similar syntax that allows
>> for specialization, whose generic implementation uses dynamic_cast.
>>
>>   template<typename T, typename U>
>>   T* is(U* u) {
>>       return dynamic_cast<T*>(u);
>>   }
>
> At this point, dynamic_cast is not available because we do not
> yet have polymorphic types.  There has been some resistance to
> that notion.

Hmm, when did we rule that out?

We currently implement dynamic_cast using the poor man's simulation
based on tree_code checking.  We can just as well give such
simulation the is<> notation.

> Absent dynamic cast, we need to specialize for various type
> combinations.  Function template specialization would be handy,
> but C++ does not directly support that.  We could work around
> that.

We can always use the standard workaround: call a static member
function of a class template that can be specialized at will.

> However, in the end, the fact that try_whatever is a member
> function means that we can use a notation that depends on context
> and so can be shorter.  That is, we can write 'function' instead of
> 'cgraph_node *'.
>
> --
> Lawrence Crowl