Article about problems & suggestions for D 2.0

[Andrei Alexandrescu]

On 8/29/11 1:39 PM, Timon Gehr wrote:
> On 08/29/2011 07:44 PM, Martin Nowak wrote:
>> On Mon, 29 Aug 2011 18:55:56 +0200, Andrej Mitrovic
>> <andrej.mitrovich at gmail.com> wrote:
>>
>>> Oh man wouldn't it be cool if we could use this syntax like this:
>>>
>>> void test(R1:isInputRange, R2:isForwardRange)(R1 r1, R2 r2) {}
>>>
>>> I'm not sure how that would work with multiple constraints or
>>> constraints that need comparisons, e.g. ElementType:
>>>
>>> void test(R1:isInputRange && ElementType == int, R2:isForwardRange)() {}
>>>
>>> Just throwing ideas for D5 there.. lol.
>>
>> Well, can you come up with a useful syntax for
>> void put(E, R)(R r, E e) if(is(E : ElementType!R)) {}
>> et.al.
>>
>> Otherwise having another syntax which put the sometimes heavy template
>> constraints on the exact opposite
>> side of the function signature is not too tempting.
>
> void put(E: ElementType!R, R)(R r, E e) {}

The if-restriction on a template may build arbitrary expressions, so 
this case is addressed by pattern matching through "luck". So we 
definitely need if-restricted templates. Though I agree pattern matching 
syntax is nice, it is but an inferior alternative.

Andrei