copy and array length vs capacity. (Doc suggestion?)

[Ali Çehreli via Digitalmars-d-learn]

On 11/23/2015 04:03 PM, Steven Schveighoffer wrote:
 > On 11/23/15 4:29 PM, Jon D wrote:

 >> In the example I gave, what I was really wondering was if there is a
 >> difference between allocating with 'new' or with 'reserve', or with
 >> 'length', for that matter. That is, is there a material difference
 >> between:
 >>
 >>      auto x = new int[](n);
 >>      int[] y; y.length = n;
 >
 > There is no difference at all, other than the function that is called
 > (the former will call an allocation function, the latter will call a
 > length setting function, which then will determine if more data is
 > needed, and finding it is, call the allocation function).

Although Jon's example above does not compare reserve, I have to ask: 
How about non-trivial types? Both cases above would set all elements to 
.init, right? So, I think reserve would be faster if copy() knew how to 
take advantage of capacity. It could emplace elements instead of 
copying, no?

Ali