Hi,

//remap the result blobs
foreach(k; res.blobs.keys){
int p = map(k);
if(p!=k){
res.blobs[p].weight += res.blobs[k].weight;
res.blobs.remove(k);
}
}

It boils down to:

foreach(k; aa.keys) aa.remove(k);

Is it safe, or do I have to take a snapsot of the keys range like this? ->

foreach(k; aa.keys.array) aa.remove(k); //this is 100% safe

I'm asking because I have no idea how the internal aa.keys range works. If it stores an index or a pionter inside, while I change the underlying structure of the aa, it could be a hazard...

Thanks in advance.

On Sunday, 29 August 2021 at 08:55:44 UTC, realhet wrote:

You shouldn't remove anything when iterating over .keys or .values. Use .byKey and .byValue instead to get ranges that are independent of the aa.

On Sunday, 29 August 2021 at 09:02:52 UTC, Mike Parker wrote:

I did a small test using .byKey, it's totally safe, just as you said. Thank You!

void main(){
    int[int] aa = [1:10, 2:20, 3:30];

    auto k1 = aa.keys;   auto k2 = aa.byKey;

    aa.remove(2);

    writeln(typeof(k1).stringof);  foreach(k; k1) writeln(k);
    writeln(typeof(k2).stringof);  foreach(k; k2) writeln(k);
}

On 8/29/21 5:02 AM, Mike Parker wrote:

This is exactly the opposite!

The .keys property makes a copy of all the keys and puts them into an array. Same thing with .values. It is perfectly safe to remove anything from the associative array while iterating one of those arrays.

The opposite is true for .byKey and .byValue. Those yield a range iterating over the actual data in the associative array. Removing an element while iterating one of those could potentially iterate over null or stale data, do not do this. While this might work out in some tests, eventually you will get bit by this, especially if you remove an element you are currently iterating.

-Steve

On Sunday, 29 August 2021 at 11:09:28 UTC, Steven Schveighoffer wrote:

Sorry about that. I can't believe I mixed those up.