// rdmd -unittest -main -dip25 dip25.d

private struct Container
{
	this(int c) @safe
	{
		arr = new int[](c);
		arr[] = c;
	}

	~this() @safe
	{
		arr[] = -1;
	}

	ref Range opSlice() return @safe // remove "return" and this code correctly fails to compile
	{
		r.index = 0;
		r.c = &this;
		return r;
	}

	@safe struct Range
	{
		int front() { return c.arr[index]; }
		bool empty() { return index >= c.arr.length; }
		void popFront() { index++; }
		size_t index;
		Container* c;
	}

private:
	Range r;
	int[] arr;
}

private struct S
{
	void takesContainer(ref Container c) @safe
	{
		this.r = c[];
	}

	void print() @safe
	{
		import std.stdio:writeln;
		writeln(r);
	}

	Container.Range r;
}

void doStuff(ref S s) @safe
{
	auto c = Container(20);
	s.takesContainer(c);
}

@safe unittest
{
	S s;
	doStuff(s);
	s.print();
}