cast(string) for mutable array

[Richard (Rikki) Andrew Cattermole]

On 01/08/2026 3:10 AM, H. S. Teoh wrote:
> On Fri, Jul 31, 2026 at 02:53:23PM +0000, user1234 via Digitalmars-d-learn wrote:
>> On Friday, 31 July 2026 at 13:52:12 UTC, Vindex9 wrote:
>>> Is this code normal? Why can't it be marked with `@safe`? Can only
>>> `idup` be used for `@safe` in such cases?
>>>
>>> ```d
>>> string fn() @trusted pure {
>>>      char[] arr;
>>>      // some manipulations...
>>>      return cast(string) arr;
>>> }
>>> ```
>>>
>>> Where is the line between cases where the `@trusted` tag can be used and
>>> cases where the `@system` tag can be used?
> [...]
> 
> If the function is pure, you should be able to just return char[] and
> the caller will be able to assign it to string.  No need for a cast.
> Just specify the return type as `char[]`.
> 
> 
> T

```d
string foo(ref char[] val) pure {
	char[] temp;
	temp ~= '2';

	val = temp;
	return cast(string)temp;
}
```

And this is why it isn't special cased and allowed to happen.

Pure in D isn't very strong.