I want to add a Phobos module with template mixins for common idioms.

[Steven Schveighoffer]

On Mon, 06 May 2013 17:13:00 -0400, Idan Arye <GenericNPC at gmail.com> wrote:

> On Monday, 6 May 2013 at 19:47:33 UTC, Diggory wrote:
>> It's a nice idea but personally I don't like the syntax much, for  
>> example it's completely non-obvious what "true" does when passed to the  
>> singleton mixin, or that the parameters to the property mixin are  
>> "type, name, condition, initial value".
>>
>> I suppose you could do something like this:
>> mixin property!`int x = 1`;
>>
>> The other problem is that I don't think it's beneficial to invite the  
>> use of mixins for such simple substitutions. I'd rather see the  
>> majority of code be standard D syntax, and the use of mixins be the  
>> exception rather than the rule. It's similar to how excessive use of  
>> macros in C++ is generally considered bad practice.
>
> If D supported Java's annotation metaprogramming I could have  
> implemented a syntax like:
>
>      @Property(`a < 50`) int a = 1;
>
> since it doesn't, I have to use mixin templates...

D supports @Property syntax (though I would suggest a different  
identifier) via User-defined-attributes.  However, you will still need the  
mixin, I don't think it can add code.

This brings up a good idiom though.  Since mixin is the only thing that  
can inject code, but its usage is ugly, @uda's can be useful for  
specifying nice parameters to the mixin, and you could have one mixin per  
class instead of per property.  I think Manu uses this to great effect  
(was in his first talk).

-Steve