The Next Big Language

[Justin Johansson]

On 19/10/2010 10:29 PM, bearophile wrote:
> Justin Johansson
>
>> There is also a big problem with reconciling templated types with OO typed hierarchies.  Often a dichotomy appears when templates and classes seem to fight one another when you try to marriage the two idioms together (for better or for worse but generally worse). :-(<
>
> Right.
>
> -------------
>
> Peter Alexander:
>
>> I think it has very little to do with the syntax (although it certainly plays a part).
> The real problem with templates (in my opinion) is that they require a higher level abstract view of programs that most programmers simply lack. I think this is the same reason why functional programming escapes the masses, and why C is still so popular.<
>
> Some of the problems of C++ templates:
> - The syntax is a big problem; if you want to use them to do complex things you need to write lot of ugly code. The lack of basic constructs like static if doesn't help at all.
> - The semantics is not clean, there are several corner cases, that turn template programming into a puzzle solving activity.
> - C++ templates are a functional language, but the C++ compilers usually lacks the normal tools a functional language needs, like a garbage collector and an optimizer both designed for a functional language, and error messages good for a functional language. This makes then slow for the compiler, and at compile-time the compiler burns lot of RAM (they have improved a bit G++ 4.5, as template instantiations are now looked up using hash tables: http://cpptruths.blogspot.com/2010/03/faster-meta-programs-using-gcc-45-and.html  but it's a long way to go).
> - C++ templates are powerful, because templates templates are a peek into the realm of higher order types (kinds), but there is not much typing on the types, so bugs are common. The Concepts were a way to add a type system to template arguments, but it has failed.
> - C++ programmers sometimes don't know much about functional programming. But in the end the complexity of functional programs written with C++ templates is very limited, they are often almost trivial. What makes them hard to write is not that, it's the way you have to write such little functional programs.
>
> D2 improves the situation a bit (with constraints, a more consistant semantics, a bit better syntax, static ifs, more template argument types, and some shortcuts), but there's a long way to go still. Despite the constraints D templates are still "dynamically kinded" (the enforcement is one way only, not two way as in the Concepts, you may solve the problem a bit manually, as Andrei has shown me), the compile-time GC is not good enough yet, lot of useless stuff is left in the final binaries, etc.
>
> D2 templates too may cause bloat, because there is no way to choose where you want Java or C# style generics with auto-boxing and where you want C++-style templates (this may be good anyway, to keep both language and compiler simpler).
>
> Bye,
> bearophile


You are a smart person bearophile, much smarter than me.
Cheers, Justin