Memoize and other optimization.

[bearophile]

David:

> Is using std.functional.memoize useful for that function, or is 
> the lookup slower?

This is hard to tell, in general you have to write two versions 
of your code, and time them.


> PS:/ I just noticed that I wanted to optimize "arr ~= …". 
> Better using a static array or std.array.appender with reserve?

A static array, where usable, is faster because it has no resize 
costs. appender is supposed to be faster than ~= if you are 
appending a lot, but unfortunately this is not always true, and 
you have to time again.

Bye,
bearophile