Compiler bug or incorrect usage for pointer of Struct?

[Temtaime]

On Sunday, 14 January 2018 at 04:02:09 UTC, Heromyth wrote:
> 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);
> 	}
> }

https://run.dlang.io/is/RUHtqK
It's not ok dude
It runs because you don't use any variable inside the struct and 
because struct members are simple functions with hidden parameter