On Saturday, 28 January 2017 at 11:54:58 UTC, cym13 wrote:
I am trying to wrap my head around lazy evaluation during
filtering/mapping, but there's something I don't understand.
I want to create an array, square some elements, remove some
elements from original array and add the squared ones to the
original array:
import std.stdio, std.algorithm, std.array;
int[] arr;
foreach (i; 0..10)
arr ~= i;
writeln("Original array: ",arr);
// [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] -- OK
auto arrMap = arr.filter!(x => x > 5).map!(x => x^^2);
writeln("arrMap: ", arrMap);
// [36, 49, 64, 81] -- OK
int[] toRemove = [1, 2, 9];
arr = arr.remove!(x => toRemove.canFind(x)).array;
writeln("Original array after removal: ", arr);
// [0, 3, 4, 5, 6, 7, 8] -- OK
arr ~= arrMap.array;
writeln("Original array after removal and concatenation: ",
arr);
// [0, 3, 4, 5, 6, 7, 8, 64, 49, 64, 81] -- what?
The last result is not what I wanted. I would expect [0, 3, 4, 5,
6, 7, 8] and [36, 49, 64, 81] concatenated into [0, 3, 4, 5, 6,
7, 8, 36, 49, 64, 81], but something else is happening here.
It looks like arr = arr.remove!.... is messing things up, but
why?
