On 12/16/2017 03:58 PM, Steven Schveighoffer wrote:
I think you are fine to just use Array and not worry about the
reallocations, they are handled automatically.
-Steve
I was going to suggest the same to Vino and I was writing the following
program to demonstrate how low the number of allocations is.
I don't remember whether this was discussed but I would additionally
suggest staying with D's native arrays. I know Array does not use the GC
for it's buffer but I don't know why it would matter in a program where
one already calls byLineCopy, .array, etc.
Further, as the program below demonstrates, native arrays are better
when it comes to memory allocation: For 1 million elements, Array!int
made 33 allocations and int[] made 24 allocations. (Of course I know 33
== 24 in this case. :) )
import std.stdio;
import std.container;
void main() {
test!(Array!int)();
test!(int[])();
}
void test(A)() {
writefln("\n--- Testing %s ---", A.stringof);
A arr;
size_t allocations = 0;
bool dotPrinted = false;
enum N = 1_000_000;
foreach (i; 0 .. N) {
string mark = " ";
const oldCapacity = arr.capacity;
arr ~= i;
if (arr.capacity != oldCapacity) {
++allocations;
mark = " <--";
}
if ((i < 10) || (i >= N - 10)) {
writefln("length:%4s capacity:%4s %s allocations: %s
alloc/item: %f",
arr.length, arr.capacity, mark, allocations,
double(allocations)/(i + 1));
} else if (!dotPrinted) {
writefln("[... %s more lines here ... ]", N - 2 * 10);
dotPrinted = true;
}
}
}
--- Testing Array!int ---
length: 1 capacity: 1 <-- allocations: 1 alloc/item: 1.000000
length: 2 capacity: 2 <-- allocations: 2 alloc/item: 1.000000
length: 3 capacity: 4 <-- allocations: 3 alloc/item: 1.000000
length: 4 capacity: 4 allocations: 3 alloc/item: 0.750000
length: 5 capacity: 7 <-- allocations: 4 alloc/item: 0.800000
length: 6 capacity: 7 allocations: 4 alloc/item: 0.666667
length: 7 capacity: 7 allocations: 4 alloc/item: 0.571429
length: 8 capacity: 11 <-- allocations: 5 alloc/item: 0.625000
length: 9 capacity: 11 allocations: 5 alloc/item: 0.555556
length: 10 capacity: 11 allocations: 5 alloc/item: 0.500000
[... 999980 more lines here ... ]
length:999991 capacity:1049867 allocations: 33 alloc/item: 0.000033
length:999992 capacity:1049867 allocations: 33 alloc/item: 0.000033
length:999993 capacity:1049867 allocations: 33 alloc/item: 0.000033
length:999994 capacity:1049867 allocations: 33 alloc/item: 0.000033
length:999995 capacity:1049867 allocations: 33 alloc/item: 0.000033
length:999996 capacity:1049867 allocations: 33 alloc/item: 0.000033
length:999997 capacity:1049867 allocations: 33 alloc/item: 0.000033
length:999998 capacity:1049867 allocations: 33 alloc/item: 0.000033
length:999999 capacity:1049867 allocations: 33 alloc/item: 0.000033
length:1000000 capacity:1049867 allocations: 33 alloc/item: 0.000033
--- Testing int[] ---
length: 1 capacity: 3 <-- allocations: 1 alloc/item: 1.000000
length: 2 capacity: 3 allocations: 1 alloc/item: 0.500000
length: 3 capacity: 3 allocations: 1 alloc/item: 0.333333
length: 4 capacity: 7 <-- allocations: 2 alloc/item: 0.500000
length: 5 capacity: 7 allocations: 2 alloc/item: 0.400000
length: 6 capacity: 7 allocations: 2 alloc/item: 0.333333
length: 7 capacity: 7 allocations: 2 alloc/item: 0.285714
length: 8 capacity: 15 <-- allocations: 3 alloc/item: 0.375000
length: 9 capacity: 15 allocations: 3 alloc/item: 0.333333
length: 10 capacity: 15 allocations: 3 alloc/item: 0.300000
[... 999980 more lines here ... ]
length:999991 capacity:1048571 allocations: 24 alloc/item: 0.000024
length:999992 capacity:1048571 allocations: 24 alloc/item: 0.000024
length:999993 capacity:1048571 allocations: 24 alloc/item: 0.000024
length:999994 capacity:1048571 allocations: 24 alloc/item: 0.000024
length:999995 capacity:1048571 allocations: 24 alloc/item: 0.000024
length:999996 capacity:1048571 allocations: 24 alloc/item: 0.000024
length:999997 capacity:1048571 allocations: 24 alloc/item: 0.000024
length:999998 capacity:1048571 allocations: 24 alloc/item: 0.000024
length:999999 capacity:1048571 allocations: 24 alloc/item: 0.000024
length:1000000 capacity:1048571 allocations: 24 alloc/item: 0.000024
Ali
