struct MyType
{
    void* ptr;
    static struct Info
    {
        @(42) int foo;
    }

    // Should be generated by the mixin below
    @property int foo()
    {
         int ret;
         getMyTypeInfo(ptr,42,int.sizeof,&ret);
         return ret;
    }
    mixin generateInfo!getMyTypeInfo;
}

extern(C) void getMyTypeInfo(void*,int, size_t,void*);

How do I write generateInfo info?

mixin template generateInfo(alias func)
{
    foreach(field; typeof(this).Info.tupleof)
    {
        //???
    }
}

I know I'll probably have to resort to string mixins, but how do I get the attribute so that I call
func(ptr,attibute, T.sizeof, &ret)? There will be a couple of values that dont have an attribute but they are all of known types and I want to handle them separately.

Thanks
Nic

On Saturday, 30 September 2017 at 08:20:44 UTC, Nicholas Wilson wrote:
> struct MyType
> {
>     void* ptr;
>     static struct Info
>     {
>         @(42) int foo;
>     }
>
>     // Should be generated by the mixin below
>     @property int foo()
>     {
>          int ret;
>          getMyTypeInfo(ptr,42,int.sizeof,&ret);
>          return ret;
>     }
>     mixin generateInfo!getMyTypeInfo;
> }
>
> extern(C) void getMyTypeInfo(void*,int, size_t,void*);
>
> How do I write generateInfo info?
>
> mixin template generateInfo(alias func)
> {
>     foreach(field; typeof(this).Info.tupleof)
>     {
>         //???
>     }
> }
>
> I know I'll probably have to resort to string mixins, but how do I get the attribute so that I call
> func(ptr,attibute, T.sizeof, &ret)? There will be a couple of values that dont have an attribute but they are all of known types and I want to handle them separately.
>
> Thanks
> Nic

You can use a struct that contains the value because apparently without you can only retrieve a specific value:

---
struct ValueHolder{int value;}

struct Foo
{
    @ValueHolder(42) int foo;

    int getTheValueDuringTheCall(string member)()
    {
        import std.traits;
        alias uda = getUDAs!(__traits(getMember, Foo, member), ValueHolder);
        static if (uda.length == 1)
            return uda[0].value;
        else
            return 0;
    }

    void test()
    {
        import std.stdio;
        writeln(getTheValueDuringTheCall!"foo");
    }
}

void main()
{
    Foo foo; foo.test();
}
---

I mean that `getUDAs!(__traits(getMember, Foo, member), int);` wouldn't work.