Suggestion: function template overloading

[Sean Kelly]

Kristian wrote:
> On Tue, 29 Aug 2006 21:04:53 +0300, Sean Kelly <sean at f4.ca> wrote:
> 
>> Kristian wrote:
>>>  It would be very nice if you could overload function templates as 
>>> you can in C++. Here is what I mean:
>>>  void f(T)(T val) {...}
>>>  void f(int val) {...}  //error: conflicts with the template function
>>>  It would allow you to write special cases for types that need it.
>>
>> void f(T)(T val) {}
>> void f()(int val) {}
>>
>>
>> Sean
> 
> Ah, thanks! I missed _that_ one completely... :/
> 
> But now I can't get the following to work:
> 
> bool equal(T)(T l, T r) {
>     return l == r;
> }
> bool equal()(Foo l, Foo r) {
>     return l.m_val == r.m_val;
> }
> 
> class Foo {
>     int m_val = 0;
> }
> 
> class Bar(T) {
>     this() {
>         m_val = new T;
>     }
> 
>     bool eq(T obj) {
>         return(equal(m_val, obj));  //error: matches more than one 
> template, equal(T) and equal()
>     }
> 
>     T m_val;
> }
> 
> void main() {
>     Bar!(Foo) bar = new Bar!(Foo);
>     Foo foo = new Foo;
> 
>     printf("%d\n", bar.eq(foo));
> }
> 
> It seems that 'binding' is done when 'Bar' is compiled, not when 'bar' 
> variable is declared.

In this case, it should choose equal()( Foo ... ) over equal(T)( T ...) 
because the Foo overload is the most specialized for the supplied 
parameters.  Unfortunately, implicit template support in DMD is still 
pretty thin so you're probably running into a compiler limitation rather 
than a problem with the spec.  Instead of:

equal()( Foo l, Foo r )

try:

equal( T : Foo )( Foo l, Foo r )

and see what happens.  I've found that with a bit of experimentation 
(and perhaps some wrapper code) you can usually get ITI to work as 
desired, and simply remove the work-around code as DMD improves.


Sean