On 06/04/2013 09:19 PM, Idan Arye wrote:
Consider the following code. What will it print?
auto arr=new ulong delegate()[5];
foreach(i;0..arr.length){
arr[i]=()=>i;
}
writeln(arr.map!`a()`());
It is natural to expect that it will print [0, 1, 2, 3, 4], but it
actually prints [5, 5, 5, 5, 5]. The reason is obvious - all the
delegates refer to the same `i` in their closures, and at the end of the
loop that `i` is set to `5`.
...
It is not that obvious. They refer to different i's that happen to
reside at the same place in the stack frame. It's a bug.
It is more obvious that it is a bug given this code snippet:
import std.stdio, std.algorithm;
void main(){
auto arr=new ulong delegate()[5];
foreach(immutable i;0..arr.length){
arr[i]={auto j=i;return {assert(j==i); return i;};}();
}
writeln(arr.map!`a()`());
}
As you can see, 'i' mutates even though it is declared immutable.
...
Yes. Yes.
http://d.puremagic.com/issues/show_bug.cgi?id=2043
