What's wrong with D's templates?

[BCS]

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)