On Wed, Sep 19, 2012 at 11:39 AM, Lawrence Crowl <cr...@googlers.com> wrote:
> On 9/19/12, Gabriel Dos Reis <g...@integrable-solutions.net> wrote:
>> On Sep 19, 2012 Richard Guenther <richard.guent...@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.
>
> Absent dynamic cast, we need to specialize for various type
> combinations.
The generic implementation can simply assert.
template<typename T> bool symbol::is()
{
assert (0);
return true;
}
template <> bool symbol::is<function>()
{
if (type_ == FUNCTION)
return true;
return false;
}
template <> bool symbol::is<variable>()
{
if (type_ == FUNCTION)
return false;
return true;
}
David
> Function template specialization would be handy,
> but C++ does not directly support that. We could work around
> that. 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
