templategroupby.d

alias seq(T...)=T;
template groupby(alias F,A...){
    template groupby(int I){
        alias groupby=seq!();
        static foreach(J,a;A){
            static if(F(J)==I){
                groupby=seq!(groupby,a);
            }
    }}
}
unittest{
    import std;
    alias foo=groupby!(a=>a%2,int,float,bool,1,2,3,13.37);
    foo!0.stringof.writeln;
    foo!1.stringof.writeln;
    alias bar=groupby!(a=>a/3,int,float,bool,1,2,3,13.37);
    bar!0.stringof.writeln;
    bar!1.stringof.writeln;
    bar!2.stringof.writeln;
}