[Issue 17331] appender can't be used for initialization twice

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=17331

--- Comment #2 from Tomáš Chaloupka <chalucha at gmail.com> ---
My guess is that problem is here:
https://github.com/dlang/phobos/blob/master/std/array.d#L2884

As this constructor is called when appender is used with null arr parameter.
So I guess that in CTFE _data is set to the same struct pointer?

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