Walter's DConf 2014 Talks - Topics in Finance

[deadalnix]

On Sunday, 23 March 2014 at 17:38:17 UTC, Sean Kelly wrote:
> On Saturday, 22 March 2014 at 14:04:01 UTC, Daniel Davidson 
> wrote:
>>
>> For example, I could see technical reasons why in certain 
>> non-quant areas like XML parsing where D can be faster than 
>> C++. 
>> (http://dotnot.org/blog/archives/2008/03/12/why-is-dtango-so-fast-at-parsing-xml/) 
>> But then, with a large amount of time and unlimited funding 
>> the techniques could probably be duplicated in C++.
>
> Try no funding and a trivial amount of time.  The JSON parser I 
> wrote for work in C performs zero allocations and unescaping is 
> performed on demand.  D arguably makes this easier by building 
> slicing into the language, but not decoding or copying is a 
> design decision, not a language artifact (at least in the case 
> of C/C++ where aliasing data is allowed).  The take-away from 
> that Tango article is that the performance hit for parsing is 
> aggressively decoding data the user may not care about or may 
> not want decoded in the first place.  This just happens to be 
> the approach that basically every XML parser on the planet uses 
> for some ridiculous reason.

This isn't for ridiculous reasons, this is because in other 
languages you have no guarantee that what you work on is 
immutable. So you must aggressively copy anyway. With a separate 
decoding step, you'll ends up copying twice, which is also 
wasteful.