Metaprogramming in D : Some Real-world Examples

[Andrei Alexandrescu]

grauzone wrote:
> Don wrote:
>> Christopher Wright wrote:
>>> grauzone wrote:
>>>> You're not testing for types, you're testing if it compiles. Inside 
>>>> the tested block of code, all sorts of things could go wrong. You 
>>>> can't know if is(typeof(...)) really did what you wanted, or if 
>>>> something broke.
>>
>> You're testing, "is everything inside that OK?". If you want to know 
>> WHY it's wrong, you'd better make sure you're testing something simple.
> 
> Andrei's range lib uses it more in a way "does this type support this 
> and that range interface?". Example: 
> http://dsource.org/projects/phobos/browser/trunk/phobos/std/range.d#L58

Then different isXxxRange are used by higher-order ranges in defining 
refined interfaces depending on the interfaces offered by their inputs. 
I fail to see how that's terrible. I am very happy D has that feature - 
no other statically-typed language has it, and it can be used to great 
effect. Look e.g. at Chain:

http://dsource.org/projects/phobos/browser/trunk/phobos/std/range.d#L799

There, the uses of static if (is(...)) allow Chain to define as capable 
an interface as its inputs allow.


Andrei