Sjoerd van Leent wrote:
As D is typically a system language, this enhancement might not make it, but I
still think it would be practical.
I've been thinking of a real world example for this, and yesterday found a nice
example to illustrate.
Suppose you would be creating an API to interrogate a database. Now within the
database, there is a table with some records. Suppose you would like to
represent this table as a D class and a record as an instance of this class (or
a struct, whatever).
class Person
{
uint id;
string first_name;
string last_name;
uint age;
}
Now, for the API to know how to use this class, it must most likely be
inheriting some kind of interface and some mapping to actually have the member
variables linked to actual columns within the table.
But it also would make the class look big and fat. So instead of that solution, might it
not be better to have a way to easily get to the member names. I was thinking of a
keyword in front of a type specification (class, struct, enum, etc.). For example, the
keyword "reflectable". (or a pragma)
reflectable class Person
{
uint id;
string first_name;
string last_name;
uint age;
}
Now the compiler knows that it has to do some magic stuff to make the fields
accessible using strings etc.
I know that it might be possible to do all of this through the vtable,
classinfo, typeinfo and so on, but it doesn't appear to be very straightforward.
http://codepad.org/1pZN2RSD
Is that what you want? That gives you the types and names of all the
properties of a struct/class. If you then want to interface with a
database with the struct or class being automatically filled out you
could use some template magic:
----
import std.string : rfind;
struct Person
{
uint id;
string first_name;
string last_name;
uint age;
}
T getFromDb(T)(string field)
{
// Code to get values from the database
}
void get( T )( ref T s )
{
foreach(k, v; s.tupleof)
{
// Used to strip off (Person ). from the property name
auto ldot = rfind( T.tupleof[k].stringof, "." ) + 1;
s.tupleof[k] = getFromDb!(typeof(v))
(T.tupleof[k].stringof[ldot..$ ]);
}
}
void main()
{
Person p;
get( p ); // P is now populated with the values from the db
}
----
