Why Templates?

[Don Clugston]

Walter Bright wrote:
> "John C" <johnch_atms at hotmail.com> wrote in message 
> news:dufl8l$14au$1 at digitaldaemon.com...
>> "Walter Bright" <newshound at digitalmars.com> wrote in message 
>> news:dufcpn$p1n$2 at digitaldaemon.com...
>>> Technically, Java and C# implement generics, not templates. C++ and D 
>>> implement templates, not generics.
>>>
>>> What's the difference? One way to think about it is generics are handled 
>>> at run time (by casting), templates at compile time.
>> I'm sure you're wrong about C#'s implementation using casts. Java generics 
>> do erase the type information and cast everything to an object. But the 
>> CLR was reworked to support generics so List<int> remains a list of ints 
>> until it's instantiated at runtime.
> 
> From what I read, C# generics do not instantiate a new routine for every set 
> of argument types, it implements *one* routine which handles them all via 
> casting. 

It looks as though it has an optimisation for built-in types.
http://www.artima.com/intv/generics2.html

Clearly C# does it a lot better than Java does. Java generics seem to be 
100% syntactic sugar.

There's a valid point raised there about the cryptic error messages 
generated in C++ templates. Currently D error messages for templates are 
even worse, but this is mainly because it keeps tying to instantiate 
templates after one has failed (and you can't even press ctrl-c to stop 
the torrent, which can last for over a minute). This is another area 
where D could give a great improvement over C++.