What's wrong with D's templates?

[Yigal Chripun]

On 18/12/2009 22:09, BCS wrote:
> Hello Yigal,
>
>> On 18/12/2009 02:49, Tim Matthews wrote:
>>
>>> In a reddit reply: "The concept of templates in D is exactly the same
>>> as in C++. There are minor technical differences, syntactic
>>> differences, but it is essentially the same thing. I think that's
>>> understandable since Digital Mars had a C++ compiler."
>>>
>>> http://www.reddit.com/r/programming/comments/af511/ada_programming_ge
>>> nerics/c0hcb04?context=3
>>>
>>> I have never touched ada but I doubt it is really has that much that
>>> can't be done in D. I thought most (if not all) the problems with C++
>>> were absent in D as this summary of the most common ones points out
>>> http://www.digitalmars.com/d/2.0/templates-revisited.html.
>>>
>>> Your thoughts?
>>>
>> I don't know Ada but I do agree with that reddit reply about c++ and D
>> templates. D provides a better implementation of the exact same
>> design,
>> so it does fix many minor issues (implementation bugs). An example of
>> this is the foo<bar<Class>> construct that doesn't work because of the
>> ">>" operator.
>> However, using the same design obviously doesn't solve any of the
>> deeper
>> design problems and this design has many of those. An example of that
>> is
>> that templates are compiled as part of the client code. This forces a
>> library writer to provide the source code (which might not be
>> acceptable
>> in commercial circumstances) but even more frustrating is the fact
>> that
>> template compilation bugs will also happen at the client.
>> There's a whole range of designs for this and related issues and IMO
>> the C++ design is by far the worst of them all. not to mention the
>> fact that it isn't an orthogonal design (like many other "features" in
>> c++). I'd much prefer a true generics design to be separated from
>> compile-time execution of code with e.g. CTFE or AST macros, or other
>> designs.
>>
>
> If D were to switch to true generics, I for one would immediately start
> looking for ways to force it all back into compile time. I think that
> this would amount to massive use of CTFE and string mixins.
>
> One of the things I *like* about template is that it does everything at
> compile time.
>
> That said, I wouldn't be bothered by optional generics or some kind of
> compiled template where a lib writer can ship a binary object (JVM
> code?) that does the template instantiation at compile time without the
> text source. (The first I'd rarely use and the second would just be an
> obfuscation tool, but then from that standpoint all compilers are)
>
>
you are confused - the term "generics" refers to writing code that is 
parametrized by type(s). it has nothing to do with JVM or the specific 
Java implementation of this idea. Java's implementation is irrelevant to 
our discussion since it's broken by design in order to accommodate 
backward compatibility.

generics != Java generics !!!

Generics are also orthogonal to meta-programming.

please also see my reply to dsimcha.