On 01/06/2018 03:08 PM, Lily wrote:
It seems a bit silly that I have to write
int[] a = [1, 2, 300, -29];
int[] b;
b.length = 4;
b[] = a[] * 2;
writeln(b);
to do what I would expect
int[] a = [1, 2, 300, -29];
writeln(a[] * 2);
to do. What am I not understanding?
So, apparently a[] * 2 is not an expression in D. It looks like such
array-wise operations require a left-hand side with memory for the results.
The reason must be for performance. If a[]*2 were an expression, the
runtime would have to allocate memory and put the results there.
Assigning that memory then to b[] would require an additional copy.
Current rule puts the burden on the programmer to find the memory. No
need to allocate if there's memory already.
However, idiomatic D delays arrays as much as possible. For example,
there is no need for destination memory for this example:
import std.stdio;
import std.algorithm;
void main() {
int[] a = [1, 2, 300, -29];
writeln(a.map!(x => 2 * x));
}
Ali
