class MyClass {
	Appender!string _stringBuilder;

	this() {
		_stringBuilder = Appender!string(null);
		_stringBuilder.clear();
	}

	@property string str() {
		return _stringBuilder.data;
	}

	void append(string s) {
		formattedWrite(_stringBuilder, "%s", s);
	}
}

MyClass c = new MyClass();
c.append("text 1");
c.append("__222");

writeln(c.str); //in this case nothing is printed out

Following workarounds work:
1) call _stringBuilder.put() instead of formattedWrite()
2) if "_stringBuilder.clear()" is omitted in the constructor, formattedWrite(...) will work as expected.

Is it a bug or is there a reason for such behaviour?

On 5/2/14, ref2401 via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com> wrote:
> class MyClass {
> 	Appender!string _stringBuilder;
>
> 	this() {
> 		_stringBuilder = Appender!string(null);
> 		_stringBuilder.clear();

Ouch, ouch, ouch! What's happening is that the 'clear' Appender method is only compiled-in if the data is mutable, otherwise you end up calling the object.clear UFCS function. So don't use clear here.

I don't know if this is a case of poor method naming or another downside of UFCS. Luckily 'clear' is being renamed to 'destroy' in the object module, so this specific case will not become a problem in the future.

On Friday, 2 May 2014 at 10:23:03 UTC, Andrej Mitrovic via Digitalmars-d-learn wrote:
> Ouch, ouch, ouch! What's happening is that the 'clear' Appender method
> is only compiled-in if the data is mutable, otherwise you end up
> calling the object.clear UFCS function. So don't use clear here.
>
> I don't know if this is a case of poor method naming or another
> downside of UFCS. Luckily 'clear' is being renamed to 'destroy' in the
> object module, so this specific case will not become a problem in the
> future.

I'd say clear should be @disabled in Appender for non-mutable data.

I logged this bug a while ago:

https://issues.dlang.org/show_bug.cgi?id=10291


On Friday, 2 May 2014 at 10:06:43 UTC, ref2401 wrote:
>
> Is it a bug or is there a reason for such behaviour?