Proposal: user defined attributes

[Adam D. Ruppe]

On Wednesday, 21 March 2012 at 13:54:29 UTC, Steven Schveighoffer 
wrote:
> I think the closest anyone has come is Jacob, with his orange 
> library.  Maybe he can respond to this point.

I have some runtime reflection in web.d, but the way I do
it is to build up the info at startup, and there's a
special field in the class to hold it.

simplified:

struct Reflection {
    string name;
    ClassInfo[string] objects;
    FunctionInfo[string] functions;
    // etc
}
class ApiProvider { immutable(Reflection)* reflection; }
immutable(Reflection)* prepareReflection(T)(T t) {
    Reflection* r = new Reflection();
    foreach(member; __traits(allMembers, T))
           static if(type..)
                 r.typeInfo[member] = prepareReflection(getMember);
}


To call functions, it makes a wrapper that converts
strings to the right types in a ParameterTypeTuple:

functionInfo.caller = wrap!func;

string delegate(string[][string]) wrap(alias func)() {
    return delegate string(string[][string] uriArgs) {
               foreach(type; ParameterTypeTuple!func)
                        blah = to!typeof(blah)(uriArgs[name]);

               return to!string(func(args));
    }
}

and so on. Of course, the real thing is a lot longer than
this, but you can see the idea.



Once it is all populated at startup, you can do:

myobj.reflection.functions["cool"].call(decodeUriVars("sweet=yes&awesome=def"));


and have it work.