updated appendable alias seq.d

--- meta.d
import std;
alias seq(T...)=T;
template appendable(discrim...){
    enum ptr_=cast(immutable(void)*)[0].ptr;
    auto poke()=>(*(cast(int*)ptr_))++;
    auto count()=>(*(cast(int*)ptr_));
    template store(int i){
    template store(T=void,T[] data=null){
        alias store=typeof(data[0]);
    }}
    template store(int i,alias A){
        alias S=store!i;
        alias store=S!A;
    }
    template append(alias A,discrim...){
        alias append=store!(poke(),A);
    }
    template opIndex(int i){
        static assert(i<count());
        alias S=store!i;
        alias opIndex=S!();
    }
    template get(discrim...){
        alias get=seq!();
        static foreach(I;0..count()){
            get=seq!(get,opIndex!I);
        }}
}
--- foo.d
import meta;
import std;
unittest{
    alias bar=appendable!();
    alias a=bar.append!int;
    alias b=bar.append!float;
    alias c=bar.append!bool;
    static assert(is(bar.opIndex!2==bool));
    bar.get!().stringof.writeln;
}