On 2/7/2014 12:46 AM, Brad Anderson wrote:
On Friday, 7 February 2014 at 08:24:39 UTC, Walter Bright wrote:
https://github.com/D-Programming-Language/phobos/pull/1911
This adds a package std.buffer, and the first entry in that package,
std.buffer.scopebuffer.
About to go to bed so just a couple of quick thoughts.
Why not just stick the stack array in ScopeBuffer itself (the
size could be a template parameter)?
1. It's set up to fit into two registers on 64 bit code. This means it can be
passed/returned from functions in registers. When I used this in my own code,
high speed was the top priority, and this made a difference.
2. It needs to avoid the default initialization of the array, because it's both
unnecessary and it kills the speed. Currently, this
cannot be avoided for part of a struct.
3. I wanted it to be usable for any block of memory the user wished to dedicate
to be a buffer.
4. Having an internal reference like that would mean a postblit is required for
copying/moving the range, another source of speed degradation.
The design of ScopeBuffer is based on a fair amount of trial and error on my
part trying to wring as much speed as possible out of it.
Also, if it did embed the static array in the ScopeBuffer I
wonder if it could just use the pointer as the buffer if the
length is less than size_t (short string optimization).
I almost never needed a buffer that small, and the extra tests for it killed
performance (I had tried it at one point).
(Just thinking aloud, I wonder if std.allocators could be used to
implement this more generically (hypothetically: alias
ScopeBuffer =
CustomAllocOutputRange!(StaticWithMallocFallbackAllocator!10)))
The custom allocator design is a long way from being realized. I don't know if
it would help or not.
It's a welcome addition and will go a long way toward cutting
down GC allocations once Phobos is output-range-ified. This technique is
probably the first thing I'd reach for when choosing an output range.
Once the buffer package is accepted, I want to add others I've been using like
circular buffers (the one from the compressor proposal), fixed buffers, and even
move std.outbuffer to it. I also want it to be one buffer design per module, not
the usual grab-bag modules.
