Hi!

I am want to get list of fields types and offsets in struct by
the template.

I.e., lookup through this struct:

struct S {

int a;
string b;
someptr* c;

};

template Lookup!( S )(); returns something as:

field #0, int, offset 0
field #1, string, offset 8,
field #2, someptr, offset 16

How I can do this?

On Sunday, 26 May 2013 at 14:19:13 UTC, mimi wrote:
> Hi!
>
> I am want to get list of fields types and offsets in struct by
> the template.
>
> I.e., lookup through this struct:
>
> struct S {
>
> int a;
> string b;
> someptr* c;
>
> };
>
> template Lookup!( S )(); returns something as:
>
> field #0, int, offset 0
> field #1, string, offset 8,
> field #2, someptr, offset 16
>
> How I can do this?

std.traits and built-in traits should do what u asking.

http://dlang.org/phobos/std_traits.html
http://dlang.org/traits.html

On Sunday, 26 May 2013 at 14:19:13 UTC, mimi wrote:
> Hi!
>
> I am want to get list of fields types and offsets in struct by
> the template.
>
> I.e., lookup through this struct:
>
> struct S {
>
> int a;
> string b;
> someptr* c;
>
> };
>
> template Lookup!( S )(); returns something as:
>
> field #0, int, offset 0
> field #1, string, offset 8,
> field #2, someptr, offset 16
>
> How I can do this?

To get a TypeTuple containing this information you can do this:

template Lookup(S)
{
    template Field(int index_, Type_, int offset_)
    {
        enum index = index_;
        alias Type = Type_;
        enum offset = offset_;
    }

    template impl(int i)
    {
        static if(i == S.tupleof.length)
            alias impl =  TypeTuple!();
        else
            alias impl = TypeTuple!(
                Field!(i, typeof(S.tupleof[i]), S.init.tupleof[i].offsetof),
                impl!(i + 1));
    }

    alias Lookup = impl!0;
}

If you only want to format this information to a string it's even simpler:

string lookup(S)()
{
    auto r = "";
    S s;
    foreach(i, e; s.tupleof)
        r ~= xformat("field #%s, %s, offset %s\n",
            i, typeof(s.tupleof[i]).stringof, s.tupleof[i].offsetof);

    return r;
}


Then lookup!S will give you the string and you can use it at compile time or at run time.

Wow! thanks!

On Sunday, 26 May 2013 at 23:37:01 UTC, mimi wrote:
> Wow! thanks!

"offsetof" will automatically distribute over the arguments so to get the offsets of a tuple you can just do:

auto tmp = TP.offsetof;

And "tmp" will be a tuple of the offsets.