return type and templates

[Andrea Fontana]

On Friday, 22 November 2013 at 10:50:58 UTC, Andrea Fontana wrote:
> On Friday, 22 November 2013 at 10:34:12 UTC, Jonathan M Davis 
> wrote:
>> On Friday, November 22, 2013 11:24:30 bearophile wrote:
>>> Jonathan M Davis:
>>> > It's not going to work for the compiler to figure out what
>>> > types might work with a given template constraint and then
>>> > have it pick one when you don't tell the template what
>>> > type to be instantiated with.
>>> 
>>> It could work if the type system become more powerful, but 
>>> what
>>> are the costs in compiler complexity, compilation times, and
>>> possible bugs in user code?
>>
>> What's it going to do? Try ever type that it knows about and 
>> see which happens
>> to work? Try every type that it sees in the template 
>> constraint (particularly
>> those in is expressions) and see if any of them work? It's a 
>> feature which
>> sounds like you're trying to write AI. I don't think that even 
>> makes sense to
>> attempt it. If there's really a type that makes sense by 
>> default, then just
>> give a default template argument. Why try and make the 
>> compiler more
>> complicated, particularly when it's questionable that it's a 
>> solvable problem,
>> and it's pretty much a guarantee that it would have a high 
>> efficiency cost even
>> if you could pull it off.
>>
>> - Jonathan M Davis
>
> I just mean:
>
> int t = s.value;  // Means  int t = s.value!int;
>
> If there's a problem with template instantiatio is the same we 
> have now.
> Now I have to write:
>
> int t = s.value!int;
>
> so if there's a problem with !int, it's just like now.
>
> It's just a syntactic sugar, no new feature... Am I wrong?

Maybe it could be extended to function call if there's no 
ambiguities.

something like;

void test(int a, long b);

test(s.value, t.value);  => test(s.value!int, t.value!long);

just if test has no abiguities with overload or template params. 
In this case we can throw an exception and template param must be 
explicit.