Daniel Keep Wrote:
>
>
> Burton Radons wrote:
> > I'm writing a couple of modules for dealing with database values (well
> > really it's just storage of aggregates) in a native fashion from within D,
> > using D 2.023. I have a tuple called FieldTypes which contains the D-side
> > types. I'm trying to use it to implement opApply:
> >
> > int opApply (int delegate (FieldTypes) func)
> >
> > Unfortunately, this fails because the compiler only accepts the field types
> > if they're references. But if I do this:
> >
> > int opApply (int delegate (ref FieldTypes) each)
> >
> > It seems that the delegate takes a reference to one type, which is a value
> > tuple! For example it claims that, simplified, "function Table.opApply (int
> > delegate (ref (string, string)) each) does not match parameter types (int
> > delegate (ref string, ref string))".
> >
> > I've already implemented another opApply that takes a Line containing all
> > the fields, but I'd like to have the expanded form as well if possible. Is
> > it?
>
> Yeah, I've run into this before. I solved it at the time using CTFE and
> string mixins:
>
> alias mixin(refDelegateFromTuple!(FieldTypes)) FieldTypesDg;
I couldn't quite figure out what you meant by this as DelegateFromTuple's not
part of Phobos from what I can tell, but I did get this going:
pure string BuildArguments (string prefix, T...) ()
{
string text;
foreach (type; T)
{
if (text.length) text ~= ", ";
text ~= prefix ~ " ";
text ~= type.stringof;
}
return text;
}
alias TypeTuple! (int, float) FieldTypes;
mixin ("alias int delegate (" ~ BuildArguments! ("ref", FieldTypes) ()
~ ") FieldTypesDeg;");
Seems to work fine, I just don't know whether "stringof" is going to be
well-behaved here. Plus it's a little extra work for the compiler.
