test.d

import std.stdio;
import std.range;
import std.algorithm;
import std.traits;


void main ()
{
    auto data = [[1,2], [3,4], [5], [6]];

    auto a = data.filter!(a=>a.length > 1);
    auto b = data.filter!(a=>a.length == 1).map!(a=>a[0]);

    writefln("%s ", a);
    writefln("%s %s", only(b), b);
    writefln("%s ", chain(a, only(b))); // error
}