Appender is ... slow

[Philippe Sigaud via Digitalmars-d-learn]

 From time to time, I try to speed up some array-heavy code by 
using std.array.Appender, reserving some capacity and so on.

It never works. Never. It gives me executables that are maybe 
30-50% slower than bog-standard array code.

I don't do anything fancy: I just replace the types, use clear() 
instead of = null...

Do people here get good results from Appender? And if yes, how 
are you using it?