Returning multiple arrays from function - struct or byref the only option?

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On Wednesday, 15 October 2014 at 16:48:24 UTC, Laeeth Isharc 
wrote:
> Hi.
>
> I have to write a bunch of functions that operate on input 
> arrays to return multiple output arrays.
>
> In case helpful the inputs are price bars or economic data 
> points (datetime, ohlc) and the outputs are nx1 arrays (I won't 
> say vectors) of doubles or structs.
>
> What is the best way to return multiple arrays in this kind of 
> situation.  In Python I returned a tuple of numpy arrays, and 
> the C way would be to pass a pointer to the return 
> destinations, and I guess I could do the same in a D way by 
> passing by ref not value).
>
> I see that I can return a struct containing dynamic arrays, and 
> return it (by value of course).  I have read the forum 
> discussion a while back over how to return multiple values, and 
> tried using tuples.  I don't see that I can return a tuple of 
> arrays - am I missing something?
>
> Here is a simple case.  Can I do better ?
>
> Thanks.
>
>
> import std.typecons;
> import std.stdio;
>
> struct RetStruct
> {
> 	double[] a;
> 	double[] b;
> }
>
> RetStruct myfunction(double x)
> {
> 	RetStruct s;
> 	double[] a,b;
> 	a~=x+1.0;
> 	a~=x+9.0;
> 	b~=x+2.0;
> 	b~=x+11.0;
> 	s.a=a;
> 	s.b=b;
> 	return s;
> }
>
> void main()
> {
> 	writefln("%s",myfunction(99.0));
> }

You could also return an std.typecons.Tuple containing both 
arrays. http://dlang.org/phobos/std_typecons.html#.Tuple