Compiler bug or incorrect usage for pointer of Struct?

[Heromyth]

On Saturday, 13 January 2018 at 14:11:23 UTC, H. S. Teoh wrote:
> On Sat, Jan 13, 2018 at 12:22:17PM +0000, Heromyth via 
> Digitalmars-d wrote: [...]
>> auto writerFor(OutRange)(auto ref OutRange outRange)
>> {
>>     auto res = Writer!(OutRange)();
>>     res.setSink(outRange);
>>     return res;
>> }
>> 
>> struct Writer(OutRange)
>> {
>>     private OutRange* output;
>> 
>>     void setSink(ref OutRange output)
>>     {
>>         this.output = &output;
> [...]
>
> Here's the bug.  `output` refers to a local variable 
> (parameter) in
> writerFor(), which goes out of scope after writerFor() exits, so
> this.output becomes a dangling pointer.
>
>
> T

I have another test. It runs whithout any error. Here it is:

import std.stdio;

void main()
{
	Tester tester = new Tester(buildWriter());
	tester.run("It's OK");
}

struct StringWriter
{
	void put(string s)
	{
		writeln(s);
	}
}

StringWriter buildWriter()
{
	return StringWriter();
}

class Tester
{
	private StringWriter* writer;

	this(StringWriter w)
	{
		writer = &w;
		writer.put("ok");
	}

	void run(string m)
	{
		writer.put(m);
	}
}