...in assert are required.

It is possible, to get similar output with standard assert using...

...main() {
    SomeClass a = new SomeClass;
    a.foo();
    assert(a.x == 1); // Fails
}

I am reopening...

...buf);

  assert(buf[0..$ - diff] == [7, 1, 2, 3]);

  swap(buf[0], rem[0]);
  assert...

...put([2]);              // <-- ERROR
  assert(arr == [1, 2, 0, 4]);

  slice.put([3]);
  assert(arr == [1...

...slice.put([2]);
  assert(arr == [1, 2, 0, 4]);

  slice.put([3]);
  assert(arr == [1...

...kinke's code and the original provided code do not assert anymore. Closing as WORKSFORME.

--

...void put(R)(R[] range, R[] source)
{
  assert(source.length <= range.length);
  foreach(element; source...

...void put(R)(R[] range, R[] source) {
  assert(source.length <= range.length);
  foreach(element; source...

...void put(R)(R[] range, R[] source)
{
  assert(source.length <= range.length);
  foreach(element; source...

...RAK.length;
    auto rem = RAK.kopyala(buf);

    assert(buf[0..$ - fark] == [7, 1, 2, 3...