Cost of .dup vs. instantiation

[Chris via Digitalmars-d-learn]

On Thursday, 29 May 2014 at 12:04:35 UTC, monarch_dodra wrote:
> On Thursday, 29 May 2014 at 08:49:10 UTC, Chris wrote:
>> monarch_dodra:
>> Hm. This last point might be an issue. If I process a large 
>> input (text in this case) then I might run into trouble with 
>> "append" as a class variable. I also had a weird bug, because 
>> I didn't clear the memory for overwrite.
>
> You can always implement an "upper bound" approach, where if 
> your input data becomes larger than a certain size, you return 
> the data directly, and reset your appender. EG:
>
> Appender!(MyType[]) append;
> public auto doSomething() {
>   scope (failure) { append.clear; }
>   // ... do something
>   append ~= item;
>   MyType[] ret;
>   if (append.data.length < 10_000)
>   {
>     ret = append.data).dup;
>     append.clear; //clears buffer, keeps memory.
>   }
>   else
>   {
>     ret = append.data;
>     append = appender!(MyType[])(); //jettison old appender 
> data.
>   }
>   return ret;
> }

Yes, you're right, this is a possible solution. However, I don't 
feel good about keeping memory I don't need. This might be a 
problem when the code will finally be ported to mobile devices.

I benchmarked the two implementations (class variable vs local 
variable) and the performance (i.e. speed) remains the same.