Compile-time Interfaces

[Timon Gehr]

On 11/27/2011 12:36 PM, Jacob Carlborg wrote:
> On 2011-11-27 02:03, Andrei Alexandrescu wrote:
>> On 11/26/11 6:40 PM, Kapps wrote:
>>> One of the great things about D is the ability to do so much work at
>>> compile-time, including static verification. An example is the amount of
>>> constraints available for templates, static ifs, etc. But at some point,
>>> it starts getting very problematic to just figure out what something
>>> does, and what something can do. An example for this, is ranges. They
>>> can be very confusing, and you don't know what they can do without
>>> actually going and looking up the exact definition of them. Even then,
>>> you have to know that the templated type a function expects is a range.
>>> Again, very confusing, and arguably messy. Finally, even now that you
>>> know what methods you can call on this mysterious type T, and you see
>>> that there's a clause isInputRange!(T) on the method, your IDE still has
>>> no clue about any of these things making it impossible to have
>>> semi-decent code completion for that type.
>>>
>>> Which brings in, compile-time interfaces. It seems like a natural thing
>>> to include when you have the above tools. Instead of having a method
>>> such as:
>>> auto DoSomething(T)(T Data) if(isInputRange!(T)) { }
>>> You could simply do:
>>> auto DoSomething(Range Data) { }
>>> where Range is defined as:
>>> enum interface Range {
>>> void popFront() const;
>>> @property bool empty() const;
>>> @property auto front();
>>> }
>>
>> What's "auto" here? This thing alone pretty much destroys the idea;
>> we've considered it very seriously.
>>
>> Andrei
>
> "auto" cannot be used here. Just like it can't be used in any place
> where there is no implementation of a function.
>
> Seems to me it needs to look something like this:
>
> enum interface Range (T)
> {
> void popFront();
> @property bool empty() const;
> @property T front();
> }
>

The element type is not a parameter to the range interface. See 
'isInputRange'.