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?

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?