weird behave of Array?

[Adam D. Ruppe]

On Sunday, 28 July 2019 at 17:21:25 UTC, dmm wrote:
>   test(str);

The array is passed by value here, so changes to its ptr and 
length will not be seen outside the function.

However, what goes *through* the pointer - which includes the 
contents and the capacity - will be seen. The runtime tries to 
minimize weird stuff by opting for making the capacity 0 if the 
array structure has been modified in a function (so of the length 
is changed, if it is appended, etc.), so then appends will not 
stomp over contents from two different locations. Since the 
memory pointed to is a shared resource it is conservative in not 
reusing it.

You can read a bit more about this here 
https://dlang.org/articles/d-array-article.html#append-on (really 
the whole article might be good background).