On Friday, May 11, 2012 04:45:18 mezozoysky wrote:
Hello!
I'm noticed that something non-obvious is happening with my
code
today and i've found that the trouble somewhere close to the
removing items from the dynamic arrays e.i. close to
std.algorithm.remove function in this case.
I wrote a little test example using this function:
module test.app;
import std.stdio: writefln;
import std.algorithm;
int main(string[] args) {
int[] a = [2, 4, 8, 16, 32, 64, 128];
writefln("a before: %s", a);
a.remove(3);
writefln("a after : %s", a);
a.remove(1);
writefln("a after2: %s", a);
return 0;
}
...and got the following output:
a before: [2, 4, 8, 16, 32, 64, 128]
a after : [2, 4, 8, 32, 64, 128, 128]
a after2: [2, 8, 32, 64, 128, 128, 128]
I'm confused.
Please tell me is it normal behavior of this function or is it
a
bug?
Maybe i'm doing something wrong?
Maybe i need another "remove" or maybe it's normal to use
slicing
to remove array's items (like a = a[0..i] ~ [i+1..$]) ?
Thanx for attention.
P.S. I'm sorry if my english confuses you.
No. As the documentation for remove explains, this is
completely expected.
remove removes elements from _the range_, not the container. It
can't remove
elements from the container (regardless of the container or
range type),
because it doesn't understand anything about the container. It
shifts the
elements forward in the range and returns a range which is
reduced in length
by the number of elements removed, but the original range is
not reduced in
size, nor is the underlying container reduced in size (all of
which is
slightly more confusing with dynamic arrays, because the range
_is_ the
container, which is not the case in general). Also, some ranges
don't even
_have_ an underlying container, so remove _definitely_ can't
remove anything
from the container itself - only shift elements. C++'s erase
function has the
exact same problem.
If you would just assign the result back to a, then your
example would work as
you expect.
import std.stdio: writefln;
import std.algorithm;
int main(string[] args)
{
int[] a = [2, 4, 8, 16, 32, 64, 128];
writefln("a before: %s", a);
a = a.remove(3);
writefln("a after : %s", a);
a = a.remove(1);
writefln("a after2: %s", a);
return 0;
}
a before: [2, 4, 8, 16, 32, 64, 128]
a after : [2, 4, 8, 32, 64, 128]
a after2: [2, 8, 32, 64, 128]
- Jonathan M Davis
