Hi all,

I'm trying to establish a REST API by using the type system (used in both client and server code).

Considering the code

struct Request
{
    Method method;
    string url;
    int apiLevel;
}

@Request(Method.GET, "/my-resource/%s", 1)
struct MyResourceGet
{
    @Param
    string name;

    // other members...
}

string requestUrl(ReqT)(ReqT req) if (isRequest!ReqT)
{
    import std.format : format;
    import std.traits : getSymbolsByUDA;

    Request reqAttr = RequestAttr!ReqT;

    alias paramSymbols = getSymbolsByUDA!(ReqT, Param);
    // return format(reqAttr.url, ????);
}

unittest
{
    MyResourceGet req;
    req.name = "thisone";
    assert(requestUrl(req) == "/my-resource/thisone");
}

In requestUrl, how do I actually get the value of req.name from paramsSymbols and req?

On Saturday, 26 February 2022 at 10:39:18 UTC, Remi Thebault wrote:

https://dlang.org/phobos/std_traits.html#getUDAs

On Saturday, 26 February 2022 at 11:26:54 UTC, max haughton wrote:

How do I use getUDAs in this context?
I have getUDAs!(req, Param).length == 0. I think it only works on the struct attributes, not on the fields attributes.

On Saturday, 26 February 2022 at 11:38:16 UTC, Remi Thebault wrote:

Getting the UDAs from inside a symbol must be done via a recursive procedure in the same manner one would identify the aforementioned symbol i.e. you have to go through the fields looking for UDAs then use getUDAs.

This is because UDAs cannot convey information without their context, so the trait doesn't look recursively.

On Saturday, 26 February 2022 at 12:01:14 UTC, max haughton wrote:

I don't need to get access to the UDA value, I need the value of the field decorated with UDA.
Finally I can get access to the member using __traits(getMember, req, paramSymbols[0].stringof).

On Saturday, 26 February 2022 at 17:06:06 UTC, Remi Thebault wrote:

I see, my apologies. FYI if possible you should avoid using stringof because it's basically only intended for debugging so isn't always consistent - this is what __traits(identifier) is for