Changing elements during foreach

[ixid]

On Monday, 21 October 2013 at 19:37:47 UTC, Jonathan M Davis 
wrote:
> On Monday, October 21, 2013 21:16:00 qznc wrote:
>> On Monday, 21 October 2013 at 16:22:29 UTC, Krzysztof Ciebiera
>> 
>> wrote:
>> > I understand slices now and I don't find it consistent with 
>> > "no
>> > shoot in the foot by default" statement.
>> 
>> I agree. The pitfalls are well understood, yet everybody seems 
>> to
>> love them. Ok, compared to C array they are an improvement due 
>> to
>> bounds checking. If the elements are const or immutable 
>> (string)
>> everything is fine, but write+append is basically
>> implementation-defined behavior.
>> 
>> Once there is a proper std.collections, I will probably adapt 
>> my
>> tutorial to recommend a safe alternative (ArrayList?).
>
> Just don't use slices when appending. It's only an issue when 
> you're appending
> and relying on slices continuing to refer to the same array, 
> and that's not
> going to work. Slices are primarily for reading, not writing. 
> Using a
> container doesn't change that. It just makes it so that you 
> can't even attempt
> to append to a slice, because the slice is a different type 
> than that container
> and won't support appending.
>
> - Jonathan m Davis

What would be the issue/s with disallowing appending to slices? 
So you'd have to explicitly duplicate before you could append.