Q: Help with compile time function
Myron Alexander
someone at somewhere.com
Sat Jun 23 17:24:07 PDT 2007
Hello.
I want to check that a structure contains only the supported types for a
fetch from the database. I want to check this at compile time and issue
an assert. I have come up with the following:
> /**
> * Compile time check that structure field types match supported types for
> * structure fetch.
> *
> * Supported types :-
> * int (int32), long (int64), char[] (utf-8), void[] (blob), float, double.
> *
> * Unsupported types :-
> * wchar[] (utf-16)
> * void* (null)
> *
> * It does not make sense to support null as a value return type so it will
> * never be supported. The utf16 type is not supported at this time as I do
> * not know how to support it. Only partial support for utf16 in the system.
> */
> static void chkStrucOkForFetch(T) () {
> foreach (i, f; FieldTypeTuple!(T)) {
> static assert (
> is (typeof(f) == int) || // int32
> is (typeof(f) == long) || // int64
> is (typeof(f) == char[]) || // utf-8
> is (typeof(f) == void[]) || // blob
> is (typeof(f) == float) ||
> is (typeof(f) == double)
> , "Invalid field type for structure fetch. Field ("~str(i)~
> ") not one of int, long, char[], void[], float, double."
> );
> }
> }
This code performs the check but I cannot get it to print the name of
the structure and the field.
Please can you help me with the following:
- How can I get the name of the structure (T) and field type at
compile time?
- If I call this from a normal run-time function, will it get
executed at run-time as well as in compile-time?
Thanks and best regards,
Myron.
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