Type trait alias parameters being either a string or a type

As a follow up to http://forum.dlang.org/thread/waxtzdemkuzvqdwilulj@forum.dlang.org#post-waxtzdemkuzvqdwilulj:40forum.dlang.org I'm trying to create a type trait isIndexableBy at https://github.com/nordlow/justd/blob/isIndexableBy-problem/typecons_ex.d DMD complains typecons_ex.d(78,30): Error: template instance isUnsigned!("I") does not match template declaration isUnsigned(T) typecons_ex.d(79,30): Error: template instance isIndex_!("I") does not match template declaration isIndex_(I) typecons_ex.d(91,35): Error: template instance typecons_ex.isIndexType!("I") error instantiating typecons_ex.d(95,19): instantiated from here: isIndexableBy!(int[], "I") typecons_ex.d(96,19): Error: template instance isIndexableBy!(int[3], ubyte) does not match template declaration isIndexableBy(R, alias I) typecons_ex.d(183,20): Error: template typecons_ex.indexedBy cannot deduce function from argument types !(ubyte)(int[3]), candidates are: typecons_ex.d(156,6): typecons_ex.indexedBy(alias I, R)(R range) if (isIndexableBy!(R, I)) How do I make the call isUnsigned!I return false instead of error when I is a CT string literal? Is my design sane ("D-ish")?

April 15, 2015

Re: Type trait alias parameters being either a string or a type

Posted by Nordlöw
in reply to Nordlöw

Permalink

Nordlöw

Posted in reply to Nordlöw

Permalink

On Wednesday, 15 April 2015 at 08:42:31 UTC, Nordlöw wrote:
> As a follow up to
>
> http://forum.dlang.org/thread/waxtzdemkuzvqdwilulj@forum.dlang.org#post-waxtzdemkuzvqdwilulj:40forum.dlang.org
>
> I'm trying to create a type trait isIndexableBy at
>
> https://github.com/nordlow/justd/blob/isIndexableBy-problem/typecons_ex.d
>
> DMD complains
>
> typecons_ex.d(78,30): Error: template instance isUnsigned!("I") does not match template declaration isUnsigned(T)
> typecons_ex.d(79,30): Error: template instance isIndex_!("I") does not match template declaration isIndex_(I)
> typecons_ex.d(91,35): Error: template instance typecons_ex.isIndexType!("I") error instantiating
> typecons_ex.d(95,19):        instantiated from here: isIndexableBy!(int[], "I")
> typecons_ex.d(96,19): Error: template instance isIndexableBy!(int[3], ubyte) does not match template declaration isIndexableBy(R, alias I)
> typecons_ex.d(183,20): Error: template typecons_ex.indexedBy cannot deduce function from argument types !(ubyte)(int[3]), candidates are:
> typecons_ex.d(156,6):        typecons_ex.indexedBy(alias I, R)(R range) if (isIndexableBy!(R, I))
>
> How do I make the call isUnsigned!I return false instead of error when I is a CT string literal?
>
> Is my design sane ("D-ish")?

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 IndexedBy.
Not pretty but works for now.

See
http://forum.dlang.org/thread/waxtzdemkuzvqdwilulj@forum.dlang.org#post-cirmlonzdhcryinyeyap:40forum.dlang.org

for follow-up posts.

Forums