• Myron Alexander <someone somewhere.com> Jun 23 2007
• Jari-Matti =?ISO-8859-1?Q?M=E4kel=E4?= <jmjmak utu.fi.invalid> Jun 23 2007
• Myron Alexander <someone somewhere.com> Jun 24 2007

Myron Alexander <someone somewhere.com> writes:

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.

Jari-Matti =?ISO-8859-1?Q?M=E4kel=E4?= <jmjmak utu.fi.invalid> writes:

Myron Alexander wrote:

 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?


You mean T.stringof and f.stringof ?

    - If I call this from a normal run-time function, will it get
 executed at run-time as well as in compile-time?


I'm afraid that function above doesn't do anything on runtime. You need to
use the RTTI system to get the type at runtime.

 
 Thanks and best regards,
 
 Myron.


-- 
        

Myron Alexander <someone somewhere.com> writes:

Jari-Matti Mäkelä wrote:
 
 You mean T.stringof and f.stringof ?


Exactly what I need.

 
    - If I call this from a normal run-time function, will it get
 executed at run-time as well as in compile-time?


 I'm afraid that function above doesn't do anything on runtime. You need to
 use the RTTI system to get the type at runtime.


Perfect. That is what I want.

Thanks, you have helped alot.

Regards,

Myron.