Final by default?

[Don]

On Thursday, 13 March 2014 at 19:28:59 UTC, Walter Bright wrote:
> On 3/13/2014 1:43 AM, Don wrote:
>> The worst breaking change in D2, by far, is the prevention of 
>> array stomping.
>>
>> After that change, our code still runs, and produces exactly 
>> the same results,
>> but it is so slow that it's completely unusable. This one of 
>> the main reasons
>> we're still using D1.
>
> I didn't know this. I'd like more details - perhaps I can help 
> with how to deal with it.

Our entire codebase assumes that stomping will happen. Simplest 
example:

T[] dupArray(T)(ref T[] dest, T[] src)
{
     dest.length = src.length;
     if (src.length) {
         dest[] = src[];
     }
     return dest;
}

This is equivalent to dest = src.dup, but if dest was already 
long enough to contain src, no allocation occurs.

Sure, we can add a call to "assumeSafeAppend()" everywhere. And I 
mean *everywhere*. Every single instance of array creation or 
concatentation, without exception. Almost every array in our 
codebase is affected by this.