[Article Submission] Have Your Efficiency, and Flexibility Too

[Nick Sabalausky]

"Timon Gehr" <timon.gehr at gmx.ch> wrote in message 
news:is3rb5$1g32$1 at digitalmars.com...
>
> Nick Sabalausky wrote:
>>
>> "Timon Gehr" <timon.gehr at gmx.ch> wrote in message
>> news:is2lts$2fcn$1 at digitalmars.com...
>> >
>> > @Article: A very good read, it does not get boring even though it is 
>> > quite
>> > long. I
>> > like it.
>> >
>>
>> Thanks :)
>>
>> > Small nitpick:
>> > mixin(declareInterface("IGizmo", "Gizmo!(numPorts, isSpinnable)"));
>> >
>> > It seems like this should be a mixin template, not a string mixin. Also
>> > you
>> > wouldn't normally want to specify ThisType. Use typeof(this):
>> >
>> > mixin template declareInterface(string interfaceName){
>> >    mixin(`enum _this_implements_interface_`~interfaceName~`=true;`);
>> >    mixin(`static assert(
>> >               is`~interfaceName~`!(typeof(this)),
>> >
>> >               "This type fails to implement `~interfaceName~`"
>> >           );`
>> >    );
>> > }
>> >
>> > and then you do just:
>> > mixin declareInterface!"IGizmo";
>> >
>>
>> I like the idea, but I just tried it and when I do that, 'isIGizmo' 
>> doesn't
>> seem to be able to find the '_this_implements_interface_IGizmo' (using 
>> DMD
>> 2.053). But, I wonder if that approach might be getting a little too 
>> fancy
>> for this anyway. That would definitely be the right way to go for a real
>> library, but for the article, the simpler it is to understand how it 
>> works,
>> the better, and putting string mixins inside a template mixin is more to
>> understand than just a string mixin (of course, I'm using CTFE too, but
>> that's probably conceptually simpler for most people than template 
>> mixins).
>
> Okay. Valid point. It is true that making the article more complicated is 
> not
> really an option. But you might want to add a comment that for serious 
> work,
> template mixins would be better suited (otherwise people will almost 
> certainly
> copy the string mixin approach ;))
>
> It works for me. Are you sure you did not accidentally break some other 
> part of
> your __traits(compiles,...) ?
>
> My minimal test case:
>
> template isIGizmo(T){enum isIGizmo=__traits(compiles,{static
> assert(T._this_implements_interface_IGizmo);});}
>
> mixin template declareInterface(string interfaceName){
>    mixin(`enum _this_implements_interface_`~interfaceName~`=true;`);
>    mixin(`static assert(
>
>               is`~interfaceName~`!(typeof(this)),
>
>               "This type fails to implement `~interfaceName~`"
>
>           );`
>    );
> }
>
> struct Gizmo{mixin declareInterface!"IGizmo";}
>
> static assert(isIGizmo!Gizmo);
>
> void main(){}
>

Hmm, something screwey seems to be going on. Your test example works for me 
too, but I could swear I've checked and double-checked everything (including 
the "__traits(compiles,...)") , and made your test case and my example as 
close to each other as I can, and I still can't seem to narrow down what's 
different.

I do know this: In my code, I can't use typeof(this) because the compiler 
complains that "this" is only valid inside a member function. I have no idea 
why doing that seems to work, even for me, in your test case.