Struct Flattening

[tama]

On Wed, 22 Apr 2009 13:42:27 +0900, dsimcha <dsimcha at yahoo.com> wrote:

> It's basically a tuple with some special properties.  Let's say I have a
> template struct:
>
> struct Joint(T...) {
>    T ranges;
> }
>
> It's built with:
>
> SomeType joint(T...)(T args) { // do stuff. }
>
> When one of the arguments is a Joint, I want it to flatten.  For example,
>
> Joint!(uint[], uint[]) r1;
> uint[] r2;
> auto result = joint(r1, r2);
> // result is a Joint!(uint[], uint[], uint[]), not a
> // Joint!(Joint!(uint[], uint[]), uint[]).
>
> Is there an easy metaprogramming trick that I've overlooked to make stuff
> flatten like this?

Hi,

---
import std.stdio, std.typetuple, std.traits;

struct Joint(T...)
{
     T ranges;
}

template flatten(T...)
{
     static if (T.length == 0)
         alias T flatten;
     else
         alias TypeTuple!(FieldTypeTuple!(T[0]), flatten!(T[1..$])) flatten;
}

Joint!(flatten!(T)) joint(T...)(T args)
{
     typeof(return) result;
     return result;
}

void main()
{

     Joint!(uint[], uint[]) r1;
     uint[] r2;
     auto result = joint(r1, r2);
     writeln(result);
}
---

Tested dmd 2.029 on Windows XP.

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