It is a pretty straight forward.
You tried to access memory out of bounds of the slice.
https://github.com/pascal111-fra/D/blob/main/dcollect.d#L34
That for loop is problematic in a number of ways.
You should not use int, or uint to index into memory, only size_t should
be used. It is an alias to either uint or ulong based upon the size of a
pointer.
```d
for(size_t i = ch.length - 1; i >= 0; i--)
```
Would be the corrected line.
However, it is still not correct, what happens when ch.length is zero?
It'll wrap around and become a very large number. That is most likely
what happened here.
To do this safely in D, use the foreach_reverse statement instead. There
are very few reasons to use for loops in D.
https://dlang.org/spec/statement.html#foreach-range-statement
Adjusted:
```d
foreach_reverse(i; 0 .. ch.length)
```
However this is not efficient as you are reallocating constantly.
```d
char[] ch_rev;
ch_rev.length = ch.length;
size_t offset;
foreach_reverse(c; ch)
ch_rev[offset++] = c;
```
