Phobos for Review: std.buffer.scopebuffer

[Lars T. Kyllingstad]

On Friday, 7 February 2014 at 10:29:07 UTC, Walter Bright wrote:
> On 2/7/2014 2:02 AM, Lars T. Kyllingstad wrote:
>> I don't understand.  Even if your workspace is stack-based or 
>> malloc-ed, you
>> still need that one GC allocation for the return value, no?
>
> If you have a path with 20 entries in it, and don't find the 
> file, you do zero allocations instead of 20. If you find the 
> file, that's do one allocation instead of 20/2 (on average), 
> and you might be able to avoid that by passing it upwards, too 
> :-)

Ah, now I understand.  I misunderstood you -- I thought you meant 
that using ScopeBuffer to build the return array inside 
buildPath(), while retaining the function's API, would somehow 
improve its performance greatly.  But what you're saying is that 
you would change the signature as well, to something like this:

   void buildPath(IR, OR)(IR segments, OR result)
       if (isInputRange!IR && isOutputRange!(OR, char));

I fully agree, then, and I see how ScopeBuffer would be extremely 
useful if more of Phobos' functions were written like this.  In 
the specific case of buildPath(), I've actually considered 
letting the user supply their own buffer in the form of an array, 
but this is of course a more general solution.