Thread overview
Why is `Appender._data` a pointer to its `Data`-store?
October 16
Why is `Appender`'s store `Data` put directly as

    `private Data* _data;`

instead of

    `private Data _data;`

?

Removing the pointer indirection would give better locality.

If it's about optimizing for empty `Appender`s then a `Appender*` should be used in those cases instead.
October 16
On 10/16/20 5:40 PM, Per Nordlöw wrote:
> Why is `Appender`'s store `Data` put directly as
> 
>      `private Data* _data;`
> 
> instead of
> 
>      `private Data _data;`
> 
> ?
> 
> Removing the pointer indirection would give better locality.
> 
> If it's about optimizing for empty `Appender`s then a `Appender*` should be used in those cases instead.

Appender is ref counted IIRC.

-Steve
October 17
On Saturday, 17 October 2020 at 00:06:31 UTC, Steven Schveighoffer wrote:
>
> Appender is ref counted IIRC.
>
> -Steve

It's not; it uses the GC.
October 17
On 10/17/20 12:00 AM, Paul Backus wrote:
> On Saturday, 17 October 2020 at 00:06:31 UTC, Steven Schveighoffer wrote:
>>
>> Appender is ref counted IIRC.
>>
> 
> It's not; it uses the GC.

Oh yeah. In fact, it was me who did that (in 2010!).

My point should have been that the appender is a pImpl to avoid memory corruption. If you have multiple copies of an appender, and each has its own idea of what the capacity is, then you will get corruption.

See the original bug report here: https://issues.dlang.org/show_bug.cgi?id=4681

-Steve