Re: Fixed-size OutBuffer that doesn't call .resize() automatically? (for database page buffers)

[Gavin Ray via Digitalmars-d-learn]

On Monday, 15 August 2022 at 22:47:21 UTC, frame wrote:
On Monday, 15 August 2022 at 20:51:07 UTC, Gavin Ray wrote:
Is there an alternative to `OutBuffer` or a method you can 
call to set a byte limit on the resizing?

Are you looking for a circular buffer?

https://code.dlang.org/packages/ringbuffer

Thanks for this suggestion, I hadn't considered it

I discovered 3 ways of doing it:

1. Calling `.toBytes()` on an `OutBuffer` will discard the extra 
bytes allocated past what was reserved and used. But this will 
still allocate the memory in the first place I guess (will the 
compiler optimize this away?)

2. Copy the `OutBuffer` class into a new `FixedSizeOutBuffer(T)` 
and alter its behavior

3. Use `ubyte[PAGE_SIZE]` and manually write like below:

```d
ubyte[] toBytes(uint value)
{
    static ubyte[4] bytes = new ubyte[4];
    bytes[0] = cast(ubyte)(value >> 24);
    bytes[1] = cast(ubyte)(value >> 16);
    bytes[2] = cast(ubyte)(value >> 8);
    bytes[3] = cast(ubyte)(value);
    return bytes;
}

void serialize(out ubyte[PAGE_SIZE] outbuf)
{
    ubyte[] buf;
    reserve(buf, PAGE_SIZE);

    buf ~= toBytes(header.pageId);
    buf ~= toBytes(header.logStorageNumber);
    buf ~= toBytes(header.prevPageId);
    buf ~= toBytes(header.nextPageId);
    buf ~= toBytes(header.freeSpacePointer);
    buf ~= toBytes(header.tupleCount);

    foreach (idx, ref slot; header.slots)
    {
        buf ~= toBytes(slot.offset);
        buf ~= toBytes(slot.size);
    }

    // Skip over free space
    ubyte[] padding = new ubyte[header.freeSpacePointer];
    padding[] = 0;
    buf ~= padding;

    foreach (idx, ref tuple; tuples)
    {
        buf ~= toBytes(tuple.size);
        buf ~= tuple.data;
    }

    move(buf.ptr, outbuf.ptr);
}
```