Array Appenders

[Denis Koroskin]

On Fri, 10 Apr 2009 11:00:01 +0400, Nick Sabalausky <a at a.a> wrote:

> "Denis Koroskin" <2korden at gmail.com> wrote in message
> news:op.ur2f3rglo7cclz at korden-pc...
>> On Wed, 08 Apr 2009 15:04:29 +0400, Frits van Bommel
>> <fvbommel at remwovexcapss.nl> wrote:
>>
>>> Andrei Alexandrescu wrote:
>>>> Denis Koroskin wrote:
>>>>> Well, actually I think that having an Appender object is an overkill.
>>>>> I never use, although I wrote a few implementations. Instead, I found
>>>>> the following method to be extemely handy, very fast and cover all my
>>>>> cases:
>>>>>
>>>>> void append(T)(T[] array, ref size_t index, T value)
>>>>> {
>>>>>    assert(array.length >= index);
>>>>>    if (array.length == index) {
>>>>>        array.length = array.length * 2;
>>>>>    }
>>>>>        array[index++] = value;
>>>>> }
>>>>  I'm pretty sure you meant to pass array by reference.
>>>
>>> It also breaks when the array is empty.
>>
>> Yeah, I was writing from memory and could (and did!) introduce bugs.
>>
>> My intend was to show an easy way of appending to array without use of a
>> special Appender struct. I use it /very/ often and believe it belongs to
>> std.array.
>>
>
> A lot of code doesn't expect extra "unofficial" elements at the end of an
> array. Any such code would break if that append had been used on the  
> array
> it's operating on. In my experience, such code occurs often enough to  
> make
> that a dangerous strategy. You could be careful and make sure all your  
> code
> is designed in a way that accomodates such extra "allocated-but-unused"
> elements, but for all the bother that would be, you might as well just  
> use a
> real .length/.capacity solution.
>
>

Real .length and .capacity solution would be the best solution, but since slices currently lack one of these properties, I carry length outside and re-use buffer.length as capacity.

In most cases, I use this pattern for appending to a temporary buffer (which is designed to be re-used, even if it stores something). And if it stores values, then it's either 1) full and you just set "index = buffer.length;" at the beginning, or 2) size is provided ("index = initialSize;").

Never experienced any problems with it.