Burton Radons wrote:
> 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:
refDelegateFromTuple isn't in Phobos; so far as I'm aware, Phobos
doesn't contain any CTFE mixin functions.
> 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.
Looks fine to me; this is basically what I was suggesting, except I
would have made the function build the entire delegate type as a string
to clean up the calling code.
-- Daniel
