String Index Support for IndexedBy

"Nordlöw" via Digitalmars-d-learn digitalmars-d-learn at puremagic.com
Wed Apr 15 02:03:55 PDT 2015


On Tuesday, 14 April 2015 at 19:38:10 UTC, Nordlöw wrote:
> I have implemented a type constructor [Ii]ndexedBy at
>
> https://github.com/nordlow/justd/blob/master/typecons_ex.d#L97
>
> restricted by
>
> https://github.com/nordlow/justd/blob/master/typecons_ex.d#L78
>
> See unittests below for usage.
>
> I would now like to extend this to enable a variant usage as
>
>     auto xs = x.indexedBy!"I"
>
> I want this to trigger a mixin that defines a
>
>     struct I
>
> inside the struct IndexedBy.
>
> But I don't know how to change the definitions of
>
> - isIndexableBy
> - [iI]ndexedBy
>
> in order for this work.
>
> I started by replace all template arguments
>
>     I
>
> with
>
>     alias I
>
> which I believe is the way to go to make it possible for I to 
> either a type or a CT-string. But then I get lots of strange 
> compiler messages that I can't figure out what to do with.
>
> Further is my mixin attempt at
>
> https://github.com/nordlow/justd/blob/master/typecons_ex.d#L99
>
> in the right direction. If so do I have to turn IndexedBy into 
> a template mixin?
>
> Could someone please help me out here?

I managed to make it all work at

https://github.com/nordlow/justd/blob/master/typecons_ex.d#L114

by using two separate definitions of [Ii]ndexedBy for the cases 
where I is either a string literal or a type. This is not ideal 
though because it causes code duplication in the two definitions 
of IndexedBy. Can anybody come up with an alternate definition of 
[Ii]ndexedBy that doesn't required two separated definitions?


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