Function constraint vs const parameter?

[Jonathan Crapuchettes]

That worked great! I wish there was a simpler solution, but thank you very much 
for your help.
JC

Ali Çehreli wrote:
> On 06/06/2012 10:02 AM, Jonathan Crapuchettes wrote:
>  > I'm running into a problem with the following function definition when
>  > passing in a const(string[]).
>  >
>  > public T condenseCountyList(T)(const T inputList) if (is(Unqual!T :
>  > string) || is(Unqual!T : string[]))
>  >
>  > I'm getting the "Error: template common.condenseCountyList does not
>  > match any function template declaration" when calling the function as
>  >
>  > condenseCountyList(countyList);
>  >
>  > , but if I changed the calling code to
>  >
>  > condenseCountyList(cast(string[])countyList)
>  >
>  > dmd is happy.
>  >
>  > How do I need to change the function constraint to make this work?
>  >
>  > Thank you,
>  > Jonathan Crapuchttes
>
> Sorry for being terse but this works:
>
> import std.traits;
> import std.array;
>
> template isSomeStringArray(T)
> {
> enum isSomeStringArray = is (typeof(
> {
> T variable;
> static assert (isSomeString!(typeof(variable.front)));
> }()));
> }
>
> T condenseCountyList(T)(const T inputList)
> if (isSomeString!T || isSomeStringArray!T)
> {
> return T.init;
> }
>
> void main()
> {
> auto countyList = [ "Santa Clara" ];
> condenseCountyList(countyList);
> }
>
> isSomeString is defined in std.traits. isSomeStringArray above uses a number of
> D features:
>
> * anonymous delegate
>
> * executing that delegate by () (which is actually never executed)
>
> * typeof, which produces "invalid type" if the expression illegal
>
> * is, which produces true if the type that it receives is not invalid
>
> * eponymous templates
>
> Ali
>