Changing behavior of associative array

[Julian Fondren]

On Saturday, 16 December 2023 at 22:44:16 UTC, Dennis wrote:
> That's because `m[f] = 1` initializes the associative array to 
> something non-null. If you pass a `null` AA to a function which 
> adds things, the caller will still have a null pointers.

I've gotten this error in deployed Perl. Whenever the ceremony of 
creating a data structure is reduced, people can lose sight of 
when that happens.

Here's a less common gotcha:

```d
void main() {
     import std.stdio : writeln;

     int force_realloc(ref int[] seq) {
         foreach (int i; 1 .. 1_000_000) {
             seq ~= i;
         }
         return 1234;
     }

     int[] a = [4321];
     writeln(a[0]);  // 4321, of course
     a[0] = force_realloc(a);
     writeln(a[0]);  // still 4321
}
```

The `a[0]` on the left of the assignment is decided early, and 
then force_realloc() changes what the location should be.