On 11/26/10 12:22 PM, Bruno Medeiros wrote:
On 09/11/2010 01:43, Jonathan M Davis wrote:
On Monday, November 08, 2010 16:50:46 so wrote:
D arrays very powerful but you first need to understand what is going
on.
You should check the book.
An inconsistency is the copy of static arrays at assignment, but
necessary
one.
One thing i don't like about D arrays is an undefined case in dynamic
array reallocation.
It's perfectly defined, just not knowable at compile time. You can
even check the
array's capacity if you want to try and figure out when it's going to
happen.
And there's not really any reasonable alternative. What would have happen
instead? Make an array reallocate _every_ time that it's resized? That
would be
highly inefficient and could really degrade performance. Appending
becomes O(n)
instead of amortized O(1). If you're not altering the actual elements
of the
array, then the current implementation is great. If you _are_ altering
them,
then simply dup the array to guarantee that it's been reallocated.
- Jonathan M Davis
Making the array reallocate _every_ time that it's resized (to a greater
length) is actually not that unreasonable. Would it be highly
inneficient? Only if you write bad code. TDPL agrees with you, I quote:
"
One easy way out would be to always reallocate a upon appending to it
[...]
Although that behavior is easiest to implement, it
has serious efficiency problems. For example, oftentimes arrays are
iteratively grown in a loop:
int[] a;
foreach (i; 0 .. 100) {
a ~= i;
}
"
Hum, "oftentimes"? I wonder if such code is really that common (and what
languages are we talking about here?)
It would be difficult to challenge the assumption that appends in a loop
are common.
But more importantly, there is a simple solution: don't write such code,
don't use arrays like if they are lists, preallocate instead and then
fill the array. So with this alternative behavior, you can still write
efficient code, and nearly as easily.
I disagree. Often you don't know the length to preallocate (e.g. input
is from a file etc). The fact that there's a convenient append operator
only makes things more in favor of supporting such idioms. The technique
(exponential capacity growth) is well known.
The only advantage of the current behavior is that it is more noob
friendly, which is an advantage of debatable value.
I don't think the current behavior favors noobs.
Andrei
